Question

How do you evaluate `cos ((−5pi)/2)`?

Answer 1

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

Answer: zero

Explanation:

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

Answer 2

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)`