What is θ such that tanθ = -2, sinθ = 2/sqrt(5), and cosθ = -1/sqrt(5)?

I am doing a question which is not about trigonometry (but involves it in one step) and I do not know how to find theta without using a calculator. I basically want the exact value.

I would greatly appreciate it if someone could show me how to find the exact value of theta.

Thanks in advance!