Exercice 4 : -4(3x-9)+(6-7x)
= -4*3x+(-4)*9+(-4)*6-(-4)*7x
= 12x+ (-36)+(-24)+28x
=12x - 36 - 24 + 28x
= (12+28)x -(36-24)
= 40x - 12.
(-7x+3)(5+4x)
= -7x*5+(-7x)*4x+3*5+3*4x
= -35+28x+15+12x
= (28+12)x - (35+15)
= 41x - 50.
(-7x+3)(-3-7x)
= -7x*-3+(-7x)*-7x+3*(-3)+3*(-7x)
= 21x+ 49x+ (-9)+ (-21x)
= 21x+49x-9-21x
=(21+49+21)x -9
=91x-9.
