If tan(0)=-1 and 3 pi/2< 0< 2 pi, what is cos(0)?

Step-by-step explanation:

which is in 4ᵗʰ quadrant ( where only cosine and secant are positive)

now,

in short, you can see where

, in 1ˢᵗ quadrant, which is \frac{\pi}{4} and subtract that from

so

now ,

[making the triangle in the fourth quadrant]