x=x^2-30?

First you have to get all of the variables on one side:

Subratacting x from both sides gives you the equation of 0=x^2-x-30. Add 30 to both sides in order to isolate the x's: 30=x^2-x.

The closest square numbers close to 30 are 36 (6^2) and 25 (5^2).

6 works for our new equation. Let's plug it in to the original equation and make sure it works; 6=36-30. Yep, we end up with 6=6. 

x^2-x-30=0

(x-6)(x+5)=30

x=6 or x=-5

Convert to one side

factor

solve