1.(7x-2)^2 = (7x-3)(7x+2)
(=)(7x-2)²- (7x-3)(7x+2)=0
(=)49x²-28x+4-49x²-14x+21x+6=0
(=)-21x+10=0
(=)-21x=-10
(=)x=10/21
2.x(x+1)(x+2)(x+3)=24
(=)[x(x+3)](x+1)(x+2)=24
(=)(x²+3x)(x²+3x+2)=24
Đặt x²+3x=y
(=)y(y+2)=24
(=)y²+2y-24=0
(=)y²+4y-6y-24=0
(=)y(y+4)-6(y+4)=0
(=)(y-6)(y+4)=0
Thay x²+3x=y ta có
(x²+3x-6)(x²+3x+4)=0
(=)(x²+4x+4-x-2)(x²+3x+4)=0
(=)[(x+2)²-(x+2)](x²+3x+4)=0
(=)(x+2)(x+2-1)(x²+3x+4)=0
(=)(x+2)(x+1)(x²+3x+4)=0
1)x+2=0=)x=-2
2)x+1=0=)x=-1
3))(x²+3x+4)=0=)vô lý
