What is the Sin and COS

Question

If 

then  =    = 

Answer 1

sin(-5π/4) = sin(-5π/4 + 2π) = sin3π/4 = sin(π - 3π/4) = sinπ/4 = √2/2;

cos(-5π/4) = cos(-5π/4 + 2π) = cos3π/4 = - cos(π - 3π/4) = - cosπ/4 = - √2/2

We use that trig functions sin and cos have period 2π and reference angle theorem.