Maths, Optimisation, Calculus, Numerical Methods, Differential Equations.
off with the easy of these and work our way up. The first method I will talk about is estimation. It is the best way if you want a rough approximation with not too much work put into it. Just pick up a calculator and try to find a number that squares to make 6. 3? no that's 9 2.5? 6.25, closer but