Question

Factorise x2-21x+108

Answer 1

${x}^{2} - 21x + 108 \\ = {x}^{2} - 12x - 9x + 108 \\ = x(x - 12) - 9(x - 12) \\ = (x - 12)(x - 9)$

Answer 2

x^2 - 12x - 9x + 108

x(x-12) -9(x-12)

(x-9)(x-12)