đặt` √x=a`
`P=((2a^2+1)/(a^3-1)+(a)/(a^2+a+1))×((a^3+1)/(a+1)-a)`
`⇔P=(2a^2+1+a(a-1))/(a^3-1)×(a^2-a+1-a)`
`⇔P=(3a^2-a+1)/(a^3-1)×(a-1)^2`
`⇔P=(3a^2-a+1)/(a^2+a+1) ×(a-1)`
`⇔P=(3x-√x+1)/(x+√x+1) ×(√x-1)`
\begin{cases} 3x^2-2xy=160\\x^2-3xy-2y^2=8 \end{cases}
⇔\begin{cases} 3x^2=2xy+160\\x^2=3xy+2y^2+8 \end{cases}
`⇔2xy+160=3(3xy+2y^2+8)`
`⇔0=7xy+6y^2-136`
`⇔0=x^2+4xy+4y^2-144`
`⇔(x+2y)^2=144`
`⇔`\(\left[ \begin{array}{l}x+2y=12\\x+2y=-12\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=12-2y\\x=-12-2y\end{array} \right.\)
với `x=12-2y`
`⇔3(12-2y)^2-2(12-2y)y=160`
`⇔y=2`
`⇒x=12-2.2=8`
với `x=-12-2y`
`⇔3(-12-2y)^2-2(-12-2y)y=160`
`⇔y=-2`
`⇒x=12-2.2=-8`
