bjr

j'espère mettre moins de 20 minutes !

1) 2/5 + 3/4 = 2x4/5x4 + 3x5/4x5 = 8/20 + 15/20 = 33/20

2)

2 - 1/7 = 14/7 - 1/7 = 13/7

3)

12/5 x 20/9 = 12x20/5x9 = 3x4x5x4/5x3x3 = 16/3

4) 2/5 x  ? = 3

donc x = 3 x 5/2 = 15/2

=> 2/5 x 15/2 = 3

5) 8x * 7x = 56x²

6) 30% x 70 = 21

7) T = 2pi / w => w = 2pi/T

8) -3x (1-2) = -3x*1 - 3x*(-2) = -3x + 6x = 3x

9) f(x+2) ((x - 3) - 2) = (x+2) (x-5)

10) f(x) = x² - 4x

f(-2) = (-2)² - 4*(-2) = 4 + 8      tu sais