Respuesta :

(x+1)*(x+8) = x^2 + 9x + 8
(x + 1)(x + 8)

x(x + 8) + 1(x + 8)

x*x + 8*x + 1*x + 1*8

x² + 8x + x + 8

x² + 9x + 8

Hope this explains it.