(a-b)^2 = (a-b)(a-b) = a^2+b^2-2ab
N° 247
4x^2+4+8x -(4x^2+4-8x)
4x^2-4x^2+4-4+8x+8x = 16x
426)
$(x+1)^2-(x+1)(x-1)-2(x+1)$
$x^2+2x+1-(x^2-1)-2x-2$
$x^2+2x+1-x^2+1-2x-2$
$+1+1-2$
$0$
427)
$(2x+2)^2-(2x-2)^2$
$4x^2+8x+4-(4x^2-8x+4)$
$4x^2+8x+4-4x^2+8x-4$
$16x$
(a+b)^2 = (a+b)(a+b) = a^2+b^2+2ab
N° 426
x^2+1+2x-(x^2-1) -2x-2 =
x^2-x^2+2x-2x+2-2 = 0