Using the "complete the square" method, solve the following x^2 +4x - 21 =0
x2+4x-21= 0, This can be factorised into brackets as shown: (x+2)2 - 4 - 21 = 0 SImplified, so all x's are on one side of the equation: (x+2)2 = 25, Removing square root, DONT FORGET "±" : (x+2) = ± 5, Solve for two solutions: x = 3, x = -7
