Explications étape par étape:
a :
4 (1-x) (4x+9) (2x+3)=0
donc 1-x =0 ou 4x+9=0 ou 2x+3=0
donc - x = -1 4x= -9 2x = -3
x=1 x= -9/4 x = -3/2
b-
x2 - 15 x =0
x ( x - 15 ) =0
×=0 ou x -15 =0
x= 15
c-
3x + 2/ x+4 = 2
3x + 2 = 2 ( x+4)
3x + 2 = 2x + 8
3x -2x = 8 -2
x = 6
d-
( 7x-5)2 = 16
(7x - 5 )2 - 16 = 0
(7 x - 5 )2 - 4 au carré =0
( 7x - 5 - 4 ) ( 7x - 5 + 4) = 0
( 7x -9 ) ( 7x - 1 ) = 0
donc 7x - 9 =0 ou 7x - 1 =0
x = 9/7 x =1/ 7
e-
10 (x+7)(x-5)= 3x (x+7)
10 ( x+7 ) ( x-5 ) -3x ( x+7)=0
(x+7) [ 10 (x-5) - 3x] = 0
(x+7) [ 10x - 50 - 3x ] =0
(x+7) ( 7x -50 ) =0
donc x+7 =0 ou 7x - 50 =0
x = -7 7x = 50
x = 50/7
f-
x2 -81 =0
x2 - 9 au carré = 0
( x -9) ( x +9) =0
donc x-9=0 ou x+9=0
x= 9 x = -9
