Réponses

2013-06-08T08:20:21+02:00

Bonjour

 

soit x le DVD et y le CD

 

on a :3x + 25 = 47.50

3x = 47.50 -25

3x = 22.50

x = 7.50

 

le DVD coûte 7.50 et les CD 5 euros

 

N°21

a) -2x +7 = 12

     -2x = 12-7

    -2x = 5

     x = -5/2

b

-2+3y = 6

3y = 6+2

3y = 8

y = 8/3

 

c) 5-2a =12

-2a = 12-5

-2a = 7

a = -7/2

 

d) -1/2 = 3/2t -5/2

-1/2 +5/2 = 3t/2

4/2 = 3t/2

t = 4/3

 

N°25

a) 2(x+1) = 3(x-1)

2x+2 = 3x -3

2x-3x = -3-2

-x = -5 d'où x = 5

 

b) 3(2-3y) = - (y -2)

6--y = -y+2

-y+y = 2-6  donc pas de solution

 

c) -2(a-1) = 4(2a+1)

-2a+2 = 8a +4

-2a -8a = 4-2

-10a = 2

a = -2/10 = -1/5