Consider a curve given in parametric form x(t), y(t). Starting from the definition of the tangent angle (top equation set in picture).

prove the bottom half of the picture (The "dots" refer to differentiation with respect to the parameter t.

So far all I have for this problem is that since tanθ=sinθ/cosθ, that y'=sinθ and x'=cosθ, but I have no idea on how to proceed with this, and I am completely in the dark. Any help would be greatly appreciated.