Factor the following expression:
5x^2+10x-840
\(\begin{array}{lrcl} &5x^2+10x-840\\ &= 5(x^2+2x-168) \\ \text{Factorisation }& =5(x-12)(x+14)\\ &\mathbf{x_1 = 12}\\ &\mathbf{x_2 = -14} \end{array}\)
