How does cos(-pi/2)=0 and others

[subopolois]

Homework Statement

can someone tell me how cos(-pi/2)=0?
and also how-sin(-pi/2)=1?

Homework Equations

trigonometry

The Attempt at a Solution

ive tried using the two special triangles, but they haven't worked and i don't know what else to do

 

[Hootenanny]

Homework Statement

can someone tell me how cos(-pi/2)=0?
and also how-sin(-pi/2)=1?

Homework Equations

trigonometry

The Attempt at a Solution

ive tried using the two special triangles, but they haven't worked and i don't know what else to do

Notice that cosine is an even function and sine is an odd function.

Whilst it may be obvious, I will point out that the angles are in radians.