Question

What is the value ofcos pie value

Answer 1

cos(pi) = -1

You should have this memorized along with other values such as
sin(0) = 0
cos(0) = 1
sin(pi/2) = 1
cos(pi/2) = 0
sin(pi) = 0
cos(pi) = -1
sin(3pi/2) = -1
cos(3pi/2) = 0

and remember that tan = sin/cos