Exercice 1 svp urgent :/

5-(2a+5) = 5-2a-5 = -2a

-2x - (x-7x²) + (-7x+9) = -2x - x +7x² -7x+9 = 7x² - 10x + 9

7x+(5x²-5x)-(2x-7) = 7x +5x²-5x-2x+7 = 5x² +7

1/2 x² + 1/3x - 3x² + 5/3x = 1/2x² - 3x² +1/3 x +5/3x = - 5/2 x² + 2x