exercice 1: A= 16x²-24x+9 - (3x-9x²+9-27x) = 16x²-24x+9 - (9-24x-9x²) = 16x²-24x+9 - 9+24x+9x²= 5x²
exercice 2:
1) B= 16 - (x²+6x+9) = 16 - x² - 6x - 9 = -x² - 6x + 7
2) B= 4² - (x+3)² = A²-B² = (a-b)(a+b) = (4-x-3)(4+x+3)= (1-x)(7+x)
3) B = 0
(1-x)(7+x)=0
1 - x = 0 ou 7+x=0
-x= -1
x= 1 x=-7