Trigonometric function

`r^2 = x^2 +y^2` `sinθ = y/r` `=>θ = sin^(-1)(y/r)` `cosθ = x/r` `=>θ= cos^(-1)(x/r)` `tanθ = y/x` `=>θ= tan^(-1)(y/x)` `(sinθ)/(cosθ) = tanθ` `sin^2θ+cos^2θ = 1`