= 2 <=== equivalently ===> n^2 - 3n + 5 = 3^2 = 9 <=== equivalently ===> n^2 - 3n - 4 = 0 =====> factor left side <=== equivalently ===> (n-4)*(n+1) = 0 <=== equivalently ===> The roots of the last equation are 4 and -1. Check . THERE IS NO NEED TO CHECK since all transformations were equivalent (!).