2x-y=2 xy=2///////4x²-6xy+y²=?

2x-y=2 xy=2///////4x²-6xy+y²=?
2x-y=2 xy=2///////4x²-6xy+y²=?

2x-y=2 xy=2///////4x²-6xy+y²=?
4x²-6xy+y²
=（4x²-4xy+y²)-2xy
=(2x-y)²-2xy
=2²-2×2
=0

4x²-6xy+y²=4x²-4xy+y²2xy=(2x-y)^2-2xy=4-2*2=0

0

(2x-y)^2=4x^2-4xy+y^2=4,2xy=4，相减就是要求的=0

y=2x-2 带入xy=2，2x²-2x-2=0 x-½=根号五/2 x=(根号五+1)/2 y=根号五-1
所以方程式=（2x-y）²-2xy=负2