Fully simplify this equation; 3x^3 - x(3x+36) = 0

The first step is to multiply out the bracket

3x³ - 3x² - 36x = 0

Then remove the common factor 3x

3x(x² - x - 12) = 0

Then factorise the bracket, by looking for two numbers which multiply to give -12, and add to give -1

3x(x - 4)(x + 3) = 0