Помогите пожалуйста с алгеброй

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) + 7x = (3x²-3x-4x+7x-7) x (x-1) = ( 3x²-7) (x²-x)

9, (m-n) n =3 ⇒ mn -1 = 3⇒ mn = 4
(5m+2n) m = (5 + 2 * nm) = (5 + 2 * 14) = 5 12