(3x - 1)^2 = 16
3x - 1 = 4 hoặc 3x - 1 = -4
3x = 5 hoặc 3x = -3
x = 5/3 hoặc x = -1
 

nguyễn minh vũ sai nha bạn ơi

(3x - 1)^2 - 16 = (3x - 1)^2 - 4^2 = (3x - 1 - 4)(3x - 1 + 4)
b) (2x + 5)^2 - (x - 9)^2 = (2x + 5 - x + 9)(2x + 5 + x - 9)
c) 9(2x + 3)^2 - 4(x + 1) = (3(2x + 3))^2 - (2(x + 1))^2 = (3(2x + 3) - 2(x + 1))(3(2x + 3) + 3(x + 1)) 

3x - 1)^2 - 16
= (3x - 1)^2 - 4^2
= (3x - 1 - 4)(3x - 1 + 4)
= (3x-5)(3x+3)
=(3x-5).3.(x+1)
b) (2x + 5)^2 - (x - 9)^2
= (2x + 5 - x + 9)(2x + 5 + x - 9)
= (x+14)(3x-4)
c) 9(2x + 3)^2 - 4(x + 1)^2
= (3(2x + 3))^2 - (2(x + 1))^2
= [3(2x + 3) - 2.(x+1)].[3.(2x+3) +2.(x+1)]
= (6x+9-2x-2).(6x+9+2x+2)
=(4x+7)(8x+11)