How do I express complex numbers in the form reiθ?

How do I express complex numbers in the form re^iθ? Complex numbers have a general form of a+ib, i being imaginary. To answer this it is best shown on an argand diagram. Plot your complex number, then the angle at which the complex expression is plotted is your theta and its distance is "r". 

Example 3+4i

Using pythagaros we find "r": (3²+4²)^1/2=5

Using trigonometry we find "θ": tan^-1(4/3)=0.927 Rad

Therefore 3+4i is represented as 5e^0.927i