Question

[The Tri Nguyen]

Cho x^2+y^2= 1. Tinh gia tri bieu thuc: 2(x^6+y^6)-3(x^4+y^4)?

Answer 1

[LovE _ Khánh Ly_ LovE]

2(x^6+y^6)-3(x^4+y^4) 
= 2x^4(x² - 1) + 2y^4(y² - 1) - (x^4 + y^4) 
= - 2x^4 .y² - 2y^4 .x² - [(x² +y²)² - 2x².y²] 
= - 2x²y².(x² + y²) - 1 + 2x².y² 
= - 2x²y² - 1 + 2x²y² 
= - 1.