设3y=x+2z,求x²-9y²+4z²+4xz的值
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设3y=x+2z,求x²-9y²+4z²+4xz的值
设3y=x+2z,求x²-9y²+4z²+4xz的值
设3y=x+2z,求x²-9y²+4z²+4xz的值
x²-9y²+4z²+4xz
=x²+4z²+4xz-9y²
=(x+2z)²-(3y)²
因为3y=x+2z
所以
x²-9y²+4z²+4xz=0