Factorise and solve the quadratic : 3x^2 + 15x +18 = 0

First we look to see if there is a common factor in the equation. In this case there is a common factor of 3, therefore we can take 3 out as a factor. 3(x² +5x +6) = 0
The inside of the bracket is now a standard recognisable quadratic which is simple to factorise. Remember to factorise a quadratic, it is split into two brackets (x+A)(x+B), where A and B are integers. A and B here must add together to make 5, and multiply together to make 6. In this example you can see that A is 2 and B is 3. (or vice versa, it doesn't matter). For the equation to be true then either (x+3)=0 or (x+2)=0 because the factor of 3 on the outside of the bracket cannot equal 0. So the solution is x= -3 or x= -2.