A = 5x (x + 3) - 7(2-5x)
= 5x*x + 5x*3 - 7*2 - 7*(-5x)
= 5x² + 15x - 14 + 35x
= 5x²+50x - 14
b. B= (4x-1)² = (4x)² - 2*4x*1 + 1² = 16x² - 8x + 1
c. C= (3x + 5)²- (4-3x) (4+ 3x)
= (3x)²+2*3x*5 + 5² - [(4)² - (3x)²]
= 9x² + 30x + 25 - 16 + 9x²
= 18x² + 30x + 9
puisque (a+b)² = a²+2ab+b²
que (a-b)²= a²-2ab+b²
et (a+b) (a-b)² = a²-b²
