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

http://img132.imageshack.us/img132/2267/c3cprob1.jpg
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.