i was the town hall this video clip and at 5:30 \$cos fracpi2\$ is substituted through \$0\$. Using my calculator the an outcome I gained was \$-0.5\$. I m sorry one is correct?  \$cosleft(fracpi2 ight)=0\$. The reason you are getting \$-0.5\$ is since you space not placing brackets roughly \$pi/2\$. Thus, you room obtaining the value of \$(cospi)/2=(-1)/2=-0.5\$. You have to use the brackets together follows: \$cosleft(fracpi2 ight)\$.  There room a couple ways to display that \$cos (pi/2)=0\$

1) The worth \$ an(pi/2)\$ is undefined. Due to the fact that \$ an(x)=fracsin(x)cos(x)\$, and also both \$sin(x)\$ and also \$cos(x)\$ are continuous throughout the reals, this implies that it have the right to only occur if \$cos (pi/2)=0\$.

You are watching: Cos(-pi/2)

2) The co-function identification \$cos(pi/2-x)=sin(x)\$ means that \$cos (pi/2)=cos(pi/2-0)=sin(0)=0\$

3) Looking in ~ the unit circle wherein \$y=sin( heta)\$ and \$x=cos( heta)\$. Once \$ heta= 90^0=pi/2\$, \$sin ( heta)=1\$ and \$cos( heta)=0\$.

4) the derivative the \$sin(x)\$ is \$0\$ only when \$sin(x)=1\$, which just occurs as soon as \$x= fracnpi2\$ for any type of \$nin 4476mountvernon.combb N\$. Because the derivative that \$sin(x)\$ is \$cos(x)\$ this indicates that \$cos(pi/2)=cos((1)pi/2)=0\$.

If you have any qustions permit me recognize below.

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answer Mar 3 "17 in ~ 23:21 Sentinel135Sentinel135
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