Salut !
(x-5)² = (x-5)(x-5) = x*x+x*(-5)-5*x-5*(-5) = x²-5x-5x+25 = x²-10x+25
ou
identité remarquable
(x - 5)² = x²+2(x)(-5)+(-5)² = x²-10x+25
