find the exact value

Question

[2 cos _{^{inverse (-radical2/2)]}}

Answer 1

cos^-1(-√2/2) = θ means that cosθ = -√2/2 and 0 ≤ θ ≤ π

 

So, θ = 3π/4

 

Therefore, 2cos^-1(-√2/2) = 2(3π/4) = 3π/2