B= -3 x X x (-5 x X) + 2 x X x ( -7y)
=3X(-5X)+2X(-7Y)
=-15x²-14xy
C= 2t² x t + 5t x (-4t)
=2t³-20t²
D = (2 x 4 x a + 5) x (3 - 7 x a )
=(8a+5)(3-7a)
Reduis les expressions suivantes
E = 3a - (6 + 7a²) + 4a - 5
=3a-6-7a²+4a-5
=-7a²+7a-11
F = 4x(3x-6) - (2x- 9x)(3+5x)
=12x²-24x-(6x+10x-27x+45x²)
=12x²-24x-6x-10x+27x-45x²
=-33x²-13x