(2x+1)(x+1)^2 (2x+3)=18
(2x+1)(2x+3)(x^2+2x+1)=18
(2x+1)(2x+3)(x^2+2x+1)-18=0
(4x^2+8x+3)(x^2+2x+1)-18=0
[4(x^2+2x)+3](x^2+2x+1)-18=0
dat x^2+2x=y
=>(4y+3)(y+1)-18=0
4y^2+7y-15=0
4y(y+3)-5(y+3)=0
(y+3)(4y-5)=0
y+3=0 hoac 4y-5=0
y=-3,y=5/4
th1 x^2+2x=-3
x^2+2x+3=0
=>x vo nghiem vi x^2+2x+3>0 voi moi x
th2 x^2+2x=5/4
x^2+2x-5/4=0
4x^2+8x-5=0
2x(2x-1)+5(2x-1)=0
(2x-1)(2x+5)=0
2x-1=0 hoac 2x+5=0
x=1/2,x=-5/2
S={1/2;-5/2}
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