**Let’s agree again come the typical convention for labelling the parts of a right triangle. Permit the ideal angle be labelled C and also the hypotenuse c. Let A and B represent the other two angles, and a and also b the sides opposite them, respectively.**

You are watching: Given △def, which is not equal to cos(f)?

Solving right trianglesWe can use the Pythagorean theorem and also properties of sines, cosines, and tangents to resolve the triangle, that is, to uncover unknown parts in terms of well-known parts. Pythagorean theorem: a2+b2=c2. Sines: sinA=a/c, sinB=b/c. Cosines: cosA=b/c, cosB=a/c. Tangents: tanA=a/b, tanB=b/a.Let’s an initial look at some instances where we don’t know all the sides. Intend we don’t understand the hypotenuse yet we do know the other two sides. The Pythagorean to organize will offer us the hypotenuse. Because that instance, if a=10 and also b=24, then c2=a2+b2= 102+242= 100+576= 676. The square source of 676 is 26, therefore c=26. (It’s nice come give instances where the square roots come out entirety numbers; in life they generally don’t.)Now intend we know the hypotenuse and one side, yet have to discover the other. For example, if b=119 and c=169, then a2=c2–b2= 1692–1192= 28561–14161= 14400, and the square source of 14400 is 120, therefore a=120.We might only know one side but we likewise know one angle. For example, if the next a=15 and the edge A=41°, we have the right to use a sine and a tangent to find the hypotenuse and also the other side. Because sinA=a/c, we understand c=a/sinA=15/sin41. Using a calculator, this is 15/0.6561=22.864. Also, tanA=a/b, therefore b=a/tanA= 15/tan41= 15/0.8693= 17.256. Even if it is you usage a sine, cosine, or tangent counts on which side and also angle you know.Inverse trig functions: arcsine, arccosine, and arctangentNow let’s look in ~ the problem of finding angles if you understand the sides. Again, you use the trig functions, but in reverse. Here’s one example. Expect a=12.3 and b=50.1. Climate tanA=a/b=12.3/50.1=0.2455. Back when human being used tables of trig functions, they would just look increase in the tangent table to watch what angle had a tangent that 0.2455. ~ above a calculator, we use the train station trig functions named arctangent, arcsine, and also arccosine. Commonly there’s a button on the calculator labelled “inv” or “arc” the you press before pressing the suitable trig button. The arctangent that 0.2455 is 13.79, therefore the edge A is 13.79°. (If friend like, girlfriend can convert the 0.79 degrees to minutes and seconds.)That’s every there is to it.The various other three trigonometric functions: cotangent, secant, and cosecantFor many purposes the three trig attributes sine, cosine, and tangent room enough. There are, however, cases when part others space needed. In calculus, secant is frequently used. You can ask, “why six trig functions?” It’s a kind of symmetry. There are six means of make ratios of two sides of a ideal triangle, and also that offers the 6 functions:sinA=a/c (opp/hyp)cosA=b/c (adj/hyp)tanA=a/b (opp/adj)cotA=b/a (adj/opp)secA=c/b (hyp/adj)cscA=c/a (hyp/opp)You can see by the listing the cotangent (abbreviated cot, or sometimes ctn) is the mutual of tangent, secant (abbreviated sec) is the mutual of cosine, and also cosecant (abbreviated csc, or sometimes cosec) is the mutual of sine. They’re pretty lot redundant, however it’s worthwhile to recognize what they space in case you come across them. Note that cotangents are tangents of security angles, which method that cotA=tanB, and also cosecants space secants of safety angles, and that method that cscA=secB.These other three attributes can likewise be understood with the unit one diagram.

We’re considering the angle AOB. Recall the its tangent is the line AC. By the opposite the tangent that the edge FOB is the heat FG, yet FOB is the complementary angle of AOB, hence, the cotangent the AOB is FG.Next, to translate secants geometrically. The edge AOB shows up in the triangle COA together angle AOC, for this reason secAOB=secAOC=hyp/adj=OC/OA=OC. Over there you have it–the secant is the heat from the facility of the circle to the tangent heat AC. The factor it is referred to as the secant is since it cut the circle, and also the native “secant” originates from the Latin word meaning “cutting.”Similarly, the cosecant that the edge AOB is the line OG native the facility of the circle come the cotangent line FG.ExercisesNote: as usual, in all exercises on ideal triangles, c represents the hypotenuse, a and also b because that the perpendicular sides, and A and B because that the angles opposite come a and also b respectively.26.In each of the following right triangle of which two sides are given, compute the sin, cos, and also tanof the angle A and also B. Refer the results as common fractions.

You are watching: Given △def, which is not equal to cos(f)?

Solving right trianglesWe can use the Pythagorean theorem and also properties of sines, cosines, and tangents to resolve the triangle, that is, to uncover unknown parts in terms of well-known parts. Pythagorean theorem: a2+b2=c2. Sines: sinA=a/c, sinB=b/c. Cosines: cosA=b/c, cosB=a/c. Tangents: tanA=a/b, tanB=b/a.Let’s an initial look at some instances where we don’t know all the sides. Intend we don’t understand the hypotenuse yet we do know the other two sides. The Pythagorean to organize will offer us the hypotenuse. Because that instance, if a=10 and also b=24, then c2=a2+b2= 102+242= 100+576= 676. The square source of 676 is 26, therefore c=26. (It’s nice come give instances where the square roots come out entirety numbers; in life they generally don’t.)Now intend we know the hypotenuse and one side, yet have to discover the other. For example, if b=119 and c=169, then a2=c2–b2= 1692–1192= 28561–14161= 14400, and the square source of 14400 is 120, therefore a=120.We might only know one side but we likewise know one angle. For example, if the next a=15 and the edge A=41°, we have the right to use a sine and a tangent to find the hypotenuse and also the other side. Because sinA=a/c, we understand c=a/sinA=15/sin41. Using a calculator, this is 15/0.6561=22.864. Also, tanA=a/b, therefore b=a/tanA= 15/tan41= 15/0.8693= 17.256. Even if it is you usage a sine, cosine, or tangent counts on which side and also angle you know.Inverse trig functions: arcsine, arccosine, and arctangentNow let’s look in ~ the problem of finding angles if you understand the sides. Again, you use the trig functions, but in reverse. Here’s one example. Expect a=12.3 and b=50.1. Climate tanA=a/b=12.3/50.1=0.2455. Back when human being used tables of trig functions, they would just look increase in the tangent table to watch what angle had a tangent that 0.2455. ~ above a calculator, we use the train station trig functions named arctangent, arcsine, and also arccosine. Commonly there’s a button on the calculator labelled “inv” or “arc” the you press before pressing the suitable trig button. The arctangent that 0.2455 is 13.79, therefore the edge A is 13.79°. (If friend like, girlfriend can convert the 0.79 degrees to minutes and seconds.)That’s every there is to it.The various other three trigonometric functions: cotangent, secant, and cosecantFor many purposes the three trig attributes sine, cosine, and tangent room enough. There are, however, cases when part others space needed. In calculus, secant is frequently used. You can ask, “why six trig functions?” It’s a kind of symmetry. There are six means of make ratios of two sides of a ideal triangle, and also that offers the 6 functions:sinA=a/c (opp/hyp)cosA=b/c (adj/hyp)tanA=a/b (opp/adj)cotA=b/a (adj/opp)secA=c/b (hyp/adj)cscA=c/a (hyp/opp)You can see by the listing the cotangent (abbreviated cot, or sometimes ctn) is the mutual of tangent, secant (abbreviated sec) is the mutual of cosine, and also cosecant (abbreviated csc, or sometimes cosec) is the mutual of sine. They’re pretty lot redundant, however it’s worthwhile to recognize what they space in case you come across them. Note that cotangents are tangents of security angles, which method that cotA=tanB, and also cosecants space secants of safety angles, and that method that cscA=secB.These other three attributes can likewise be understood with the unit one diagram.

We’re considering the angle AOB. Recall the its tangent is the line AC. By the opposite the tangent that the edge FOB is the heat FG, yet FOB is the complementary angle of AOB, hence, the cotangent the AOB is FG.Next, to translate secants geometrically. The edge AOB shows up in the triangle COA together angle AOC, for this reason secAOB=secAOC=hyp/adj=OC/OA=OC. Over there you have it–the secant is the heat from the facility of the circle to the tangent heat AC. The factor it is referred to as the secant is since it cut the circle, and also the native “secant” originates from the Latin word meaning “cutting.”Similarly, the cosecant that the edge AOB is the line OG native the facility of the circle come the cotangent line FG.ExercisesNote: as usual, in all exercises on ideal triangles, c represents the hypotenuse, a and also b because that the perpendicular sides, and A and B because that the angles opposite come a and also b respectively.26.

**(i). C=41, a=9.(ii). C=37, a=35.(iii). A=24, b=7.31.**In a ideal triangle c=6 feet 3 inches and tanB=1.2. Find a and also b.

**34.**a=1.2, b=2.3. Discover A and also c.

**42.**a=10.11, b=5.14. Discover B and also c.In the next couple of problems, the triangles aren’t ideal triangles, yet you deserve to solve them making use of what you know around right triangles.

**61.**In an oblique triangle ABC, A=30°, B=45°, and the perpendicular from C to abdominal is 12 inch long. Uncover the size of AB.

**67.**If the next of an it is intended triangle is a, uncover the altitude, and the radii of the circumscribed and inscribed circles.

**202.**from the peak of a structure 50 feet high the angle of elevation and depression of the top and bottom of another building room 19° 41" and also 26° 34", respectively. What room the height and distance the the 2nd building.

**207.**native the peak of a lighthouse 175 feet high the angles of depression the the top and bottom the a flagpole room 23° 17" and 42° 38", respectively. Exactly how tall is the pole?

**214.**At two points 65 feet apart on the very same side the a tree and also in line v it, the angle of key of the optimal of the tree are 21° 19" and also 16° 20". Discover the elevation of the tree.

**215.**together a balloon passes between two clues A and also B, 2 miles apart, the angles of key of the balloon at this points room 27° 19" and also 41° 45", respectively. Uncover the altitude the the balloon. Take it A and B at the very same level.

**233.**The peak of a lighthouse is 230 feet above the sea. How much away is an object which is just “on the horizon”?

**234.**What should be the elevation of one observer in order the he may have the ability to see things on the planet thirty miles away? assume the planet to be a smooth sphere.In every of the figures named in the next couple of problems the thing is come express that is area (i) in terms of the radius R, the is, the radius the the circumscribed circle, (ii) in terms of the apothem r, the is, the radius the the enrolled circle, and also (iii) in regards to the side a.

**251.**it is provided triangle.

**252.**Square.

**253.**continual pentagon.

**254.**regular hexagon.

**255.**constant octagon.Hints

**26.**you only require the sin, cos, and tanof the angle A and also B; friend don’t require the angle themselves. So you only need the 3rd side, i beg your pardon you can compute with the Pythagorean theorem, and also then take it ratios of 2 of the sides.

**31.**You understand c and tanB. Unfortunately, tanB is the ratio of the two sides you don’t know, namely, b/a. There is more than one method to settle this problem. Right here are two.Method 1. Take the equation 1.2=tanB=b/a, to acquire a relation between a and also b, namely b=1.2a. The Pythagorean to organize then offers 6.252=a2+1.44a2, native which you deserve to determine a, and then uncover b.Method 2. Indigenous tanB, you can determine the angle B (use arctan). From that you can uncover cosB, and also then a, and you can find sinB, and also then b.

**34.**because you have actually a and also b, you have the right to use tangents to discover A and also the Pythagorean organize to discover c.

**42.**discover B by tangents and c by the Pythagorean theorem.

**61.**begin by drawing the figure. Return the triangle alphabet is not a appropriate triangle, the does break into two appropriate triangles. You can use tangents to find the two parts of the side abdominal and add them together.

**67.**An equilateral triangle ABC has actually three 60° crest angles. Fall a perpendicular indigenous one vertex, to speak vertex C, and also you acquire two congruent appropriate triangles ACF and also BCF, and you can find the size of that perpendicular, and also that’s the altitude that the it is provided triangle. The circumscribed one is the one passing through the 3 vertices, and the inscribed circle is the one inside tangent to the three sides. By dropping perpendiculars from the one more of the vertices that the it is provided triangle and using trig top top the resulting small triangles, friend can discover the radii the these 2 circles.

**202.**because you recognize the height of your building and angle that depression to the basic of the various other building, you deserve to determine how much away it is. Then the edge of key to the height of the other structure will phone call you exactly how much greater it is 보다 yours.

**207.**similar hint come 202. See, trig deserve to be useful if you’re a lonely lighthouse keeper and also don’t understand what come do!

**214.**This is a useful problem. You deserve to use that to find heights of inaccessible things. Attract the figure. There space two unknowns: the height y the the tree, and the street x the the nearer allude to the tree. The further suggest is then x+65 feet native the tree. Utilizing tangents of the known angles, friend can collection up two equations which have the right to be resolved to identify y and also x.

**215.**This is comparable to 214, yet in this problem, the balloon lies between the 2 points. Attract the figure. Decide on her variables. Set up equations, and also solve them.

**233.**A really interesting problem. Assorted inverses that it have actually been used for century to compute the radius of the earth. In this problem we obtain to assume we know around the earth. Every you need right here is the Pythagorean theorem. One next of a best triangle is r, the radius of the earth, and the hypotenuse is r+h whereby h is the elevation of the lighthouse. The Pythagorean theorem the third side of the triangle.

**234.**collection this trouble up comparable to 233, yet different variables space known.

**251–255.**You could do these all at once, conserving the computations for last. Let n it is in the variety of sides ~ above the constant polygon. Attract lines indigenous the facility of the number to the vertices and to the midpoints the of the sides. You obtain 2n little triangles. Each one of these is a ideal triangle with hypotenuse R, one foot r, and also the various other leg a/2. The angle at the facility is 360°/(2n)=180°/n. Making use of trigonometry, girlfriend can quickly write equations relating the area the the consistent polygon as required.Answers

**26.**(i). B = 40. For this reason sinA=cosB=9/41, cosA=sinB=40/41, tanA=9/40, tanB=40/9.

**(ii). B = 12. So sinA=cosB=35/37, cosA=sinB=12/37, tanA=35/12, tanB=12/37.(iii). C = 25. So sinA=cosB=24/25, cosA=sinB=7/25, tanA=24/7, tanB=7/24.31.**a=4 feet, b=4.8 feet, around 4"10".

**34.**A=27.55°, about 28°. C=2.6.

**42.**B=26.95°, or 26°57". C=11.3.

**61.**ab = 12/tan A + 12/tan B = 12(√3+1) inches, about 33".

**67.**(a√3)/2, (a√3)/3, and also (a√3)/6, respectively.

**202.**distance = 50/tan 26°34" = 100 feet. Height = 50 + 100 tan 19°41" = 85.8" = 85"9".

**207.**street = 175/tan 42°38" = 190 feet. Elevation = 175 - 190 tan 23°17" = 93.23" = 9"3".

**214.**The 2 equations are0.293052 = tan 16°20" = h/(65+x), and

**0.390219 = tan 21°19" = h/x.where x is the street from the nearest allude to the basic of the tree. You can solve these at the same time for x and also h.Distance x = 196". Elevation h = 76.5".215.**If h is the elevation of the balloon, and also x is the distance along the ground indigenous A come the suggest directly under the balloon, climate the two equarions aretan 27°19" = h/x, and

**tan 41°45" = h/(2–x)You deserve to solve this pair the equations because that x and also h.Height = .654 miles = 3455 feet.233.**A trifle much more than 18.5 miles.

**234.**600 feet.

**251–255.**The area of a constant n-gon is A=nra/2. To find A in regards to R, r, or a, use the relationshipscos 180°/n = r/R, andtan 180°/n = a/(2r).Then (i) in terms of R, the area A = nR2cos180°/nsin180°/n,(ii) in regards to r, the area A = nr2tan180°/n, and(iii) in terms of a, the area A = na2/(4tan180°/n).

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Problemshape(i) R(ii) r(iii) a

251 | triangle | (3R2√3)/4 | 3r2√3 | (a2√3)/4 |

252 | square | 2R2 | 4r2 | a2 |

253 | pentagon | (5R2sin108°)/2 | 5r2tan36° | (5a2tan54°)/4 |

254 | hexagon | (3R2√3)/2 | 2r2√3 | (3a2√3)/2 |

255 | octagon | 2R2√2 | 8r2tan22°30" | 2a2tan67°30" |