Đáp án+Giải thích các bước giải:
`(x^2+3x+2)(x^2+9x+18)=168x^2`
`<=>(x^2+x+2x+2)(x^2+3x+6x+18)=168x^2`
`<=>[x(x+1)+2(x+1)][x(x+3)+6(x+3)]=168x^2`
`<=>(x+1)(x+2)(x+3)(x+6)=168x^2`
`<=>[(x+1)(x+6)][(x+2)(x+3)]=168x^2`
`<=>(x^2+7x+6)(x^2+5x+6)=168x^2`
`<=>(x^2+6x+6)^2-x^2=168x^2`
`<=>(x^2+6x+6)^2-169x^2=0`
`<=>(x^2+6x+6-13x)(x^2+6x+6+13x)=0`
`<=>(x^2-7x+6)(x^2+19x+6)=0`
`<=>(x^2-x-6x+6)(x^2+19x+361/4-337/4)=0`
`<=>(x-1)(x-6)[(x+19/2)^2-337/4]=0`
`(1)=>x=1`
`(2)=>x=6`
`(3)=>x=(+-\sqrt{337}+19)/2`
