i)x^2 - 13x+40 = x² - 5x - 8x + 40 = x(x-5) - 8(x-5) = (x-5)(x-8) ;
j)x^2 - 5x+4 = x² - x - 4x + 4 = x(x-1) - 4(x-1) = (x-1)(x-4) ;
k)x^2- 8x+7 = x² - 7x - x + 7 = x(x-7) - (x-7) = (x-7)(x-1) ;
l)x^2 -12x+27 = x² - 3x - 9x +27 = x(x-3) - 9(x-3) = (x-3)(x-9);