Bonjour !
a) x(5x + 3) + x(2x + 7)
= x(5x + 3 + 2x + 7)
= x(7x + 10)
= 7x² + 10x
b)
100(13x - 8) - 100(7x - 4)
= 100(13x - 8 - 7x + 4)
= 100(6x - 4)
= 600x - 400
c)
(x + 3)(2x - 1) + (x + 3)(8x + 5)
= (x + 3)(2x - 1 + 8x + 5)
= (x + 3)(10x + 4)
= 10x² + 4x + 30x + 12
= 10x² + 34x + 12
d)
5x(3x - 4) - (3x - 4)(9x - 1)
= (3x - 4)(5x - 9x + 1)
= (3x - 4)(-4x + 1)
= -12x² + 3x + 16x - 4
= -12x² + 19x - 4
Voilà !
