How do you evaluate $cos ((−5pi)/2)$ ?

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Answer 1 · 2015-07-17T22:27:13

Evaluate $cos ((-5pi)/2)$

Answer: zero

$cos ((-5pi)/2) = cos (-pi/2 - 2pi) = cos (-pi/2) = 0$

Answer 2 · 2015-07-17T22:45:21

You can use coterminal angles and the fact that $cos(x) = cos(-x)$ , i.e. $cos$ is even. Using $2pi = (4pi)/2$ :

$cos(-(5pi)/2) = cos(-(pi)/2) = cos((pi)/2)$

$= color(blue)(cos(90^o) = 0)$

How do you evaluate cos ((−5pi)/2)cos ((−5pi)/2)?