6. 2n\ (m+n) - (m+n) \ m = ( 2mn - (m+n)² ) \ m (m+n) =
(2mn - m²-2mn-n²) \m (m+n) = - (m²+n²) \ (m²+mn)
7. (4m-3)\ (m-2) - (2m+1) \ (m-2) = (4m-3-2m-1) \ (m-2) = (2m-4) \ (m-2) =
2 (m-2) \ (m-2) = 2
8. 3 - 4\ (x-1) + 7\x = (3x²-3x-4x+7x-7) \ x (x-1) = ( 3x²-7) \ (x²-x)
9, (m-n) \ n =3 ⇒ m\n -1 = 3⇒ m\n = 4
(5m+2n) \ m = (5 + 2 * n\m) = (5 + 2 * 1\4) = 5 1\2