Hi chaps, I got a Question here that has me confused , any thoughts or help is appreciated (how do we even use a calculator to find the answer?)

Thanks(Doh)

Given that cos θ = -4/5 and π/2 ≤ θ ≤ π

find, in surd form (do not use calculators)

A) tan θ

B) Sin θ

C) sin (θ + 2π/3)

D) cos 2 θ