What is the value ofcos pie value

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