Réponse :

a) 21x² + 12x = 0

3x(7x+4)=0

7x+4=0⇔7x=-4⇔x-4/7

3x=0⇔x=0

x= -4/7 ou 0

d) 4x² - 16 = 0

(2x-4)(2x+4)=0

2x-4=0⇔2x=4⇔x=4/2=2

2x+4=0⇔2x=-4⇔x=-4/2=-2

x= 2 ou -2

b) 16x²+28x = 0

4x(4x+7)=0

4x+7=0⇔4x=-7⇔x=-7/4

4x=0⇔x=0

x= -7/4 ou 0

e) 64x² - 360 c'est 360 ou 36?

c) 25x²-9=0

(5x-3)(5x+3)=0

5x-3=0⇔5x=3⇔x=3/5

5x+3=0⇔5x=-3⇔x=-3/5

x= 3/5 ou -3/5

f) 144x² - 169 = 0

(12x-13)(12x+13)=0

12x-13=0⇔tu finis

Explications étape par étape :

bonsoir,

a) 21x² + 12x = 0

3x( 7x +4) =0

3x = 0

x= 0

7x+4 = 0

7x = -4

x=--4/7

d) 4x² - 16 = 0

(2x-2) (2x+2)=0

2x-2 = 0

2x = 2
x= 2/2

x = 1

2x+2 = 0

2x = -2

x= -2/2

x= -1

b) 16x²+28x = 0

4x ( 4x+ 7)= 0

4x= 0

x= 0

4x+7 = 0

4x = -7

x= -7/4

e) 64x² - 360

64 ( x² - 90) =0

x² = 90

x=√90

c) 25x² -9=0

( 5x -3) (5x+3) =0

5x -3=0

5x =3

x = 3/5

5x+3 = 0

5x = -3

x= -3/5

f) 144x² - 169 = 0

(12x - 13)(12x+13) = 0

12x -13 = 0

12x = 13

x= 13/12

12x+13 = 0

12x = -13

x =-13/12