Respuesta :

TheLazyNobita

x² - x - 42 = ( x+k )( x+6)

x² - 7x + 6x -42 = (x+k)(x+6)

x(x-7) + 6(x -7) = (x+k)(x+6)

(x-7)(x+6) = (x+k)(x+6)

(x+6) gets cancelled

Thus

x-7 = x+k

k = -7