2x-y=2 xy=2///////4x²-6xy+y²=?
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![2x-y=2 xy=2///////4x²-6xy+y²=?](/uploads/image/z/1333285-61-5.jpg?t=2x-y%3D2+xy%3D2%2F%2F%2F%2F%2F%2F%2F4x%26%23178%3B-6xy%2By%26%23178%3B%3D%3F)
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