Réponse :

Bonjour,

Exercice 1

1. 5a - 3 = 2 + 3a

5a-3a = 2+3

2a = 5

a = 5/2

2. A = 5/3 ( 1 -4/7) = 5/3 (7-4 /7) = 5/3 * 3 /7 = 5/7

3. f(x) = 15x + 6x² - 25 - 10x = 6x² + 5x - 25

4. Selon le théorème de Thalès, on a AM / AB = AN / AC = MN / BC

5 / AB = AN / AC = MN / 10

Or AB = AM + MB = 5 + 3 = 8

Donc 5/ 8 = MN /10

MN/10 = 5/8

MN = 5/8 * 10

MN = 50 /8 = 6.25 cm.

Exercice 2

1. Triangle à tracer.

2. 2b + 3 = 2 - 5b

2b + 5b = 2-3

7b = -1

b = -1/7

3. B = 3/5 - 4/7 + 5/3

B = 3/5 - 4*3 / 7*3 + 5*7 / 3*7

B = 3/5 - 12/21 + 35 / 21

B = 3/5 - 23/21

B = 63/105 - 115/105 = -52/105

4. f(x) = (5x -4)(7-8x) = 35x - 40x² -28 + 32x = -40x² + 67x - 28

5. Selon le théorème de thalès, on a MN / CB = AM / AC = AN/ AC

4/BC = AM/7 = 5/7

Donc 4/BC = 5/7

BC/4 = 7/5

BC = 7/5 *4

BC = 28/5

BC = 5.6