If x^4+x^2 y^2+y^4=21 and x^2+x y+y^2=3, then what is the value of (-…

x⁴ + x²y² + y⁴ = (x² – xy + y²) (x² + xy + y²)

x⁴ + x²y² + y⁴ = 21 and

x² + xy + y² = 3      --- (1)

= 21 = (x² - xy + y²) × 3

= (x² - xy + y²) = 7      --- (2)

From equation (1) from equation (2)

2xy = -4

xy = -2

-xy = 2