`{(x^3-3xy^2=10),(y^3-3x^2y=30):}`
Bình phương `2` vế:
`{((x^3-3xy^2)^2=100),((y^3-3x^2)^2=600):}`
`↔{(x^6-6x^4y^2+9x^2y^4=100),(y^6-6x^2y^4+9x^4y^2=600):}`
Cộng vế theo vế:
`x^6 - 6x^4y^2 + 9x^2y^4 + y^6 - 6x^2y^4 + 9x^4y^2 = 100 + 900`
`↔x^2+y^2=10`
Hay: `P=10`
Vậy: `P=x^2+y^2=10`
