5X²-3XY-4Y²-11XY-7X²+2Y²
=-2X²-2Y²-14XY
=-2(X²+Y²)-14XY
将X²+Y²=7,XY=-2代入,得
-2(X²+Y²)-14XY
-2×7-14×(-2)
=-14+28
=14
已知X²+Y²=7,XY=-2,求代数式5X²-3XY-4Y²-11XY-7X²+2Y²的值
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