Solve n^2 – n – 90 = 0 to find value of n
Firstly you want to factorise this expression. You have n2, so you know you want to multiple n by itself. Next, you want to think carefully about what two numbers add to get -1 (the coefficient of the second value of the expression, -n) and multiply to get -90. You have two negatives so you know one of your numbers is going to be negative and the other positive (if they were both negative you'd get +90, same if they were both positive). You'll figure out the two numbers you're looking for are - 10 and + 9 ( - 10 + 9 = -1, - 10 x 9 = - 90). So now you have(n + 9)(n - 10) = 0 For this to be true, one of the expressions on the left have to equal 0, so either n + 9 = 0 or n - 10 = 0. The possible values are therefore n = 10 or n = - 9, final answer
