There are loads of different ways to solve quadratics, and most of the time there isn't only one right way to solve them.
there's three main ways that you can use to solve quadratics: factorisation, completing the square, and the quadratic formula.
if you can see intuitively the numbers required for double bracket factorisation, then this is usually the quickest way to solve for whole number solutions.
sometimes, the numbers arent 'nice' so we need to use the quadratic formula:
x= (-b+_sqrt(b2-4ac))/2a
for an equation ax2+bx+c=0
this will give solutions to any quadratic.