x减y的差的2次方等于多少 91的2次方减(x-y)的2次方等于多少
\uff08x-y\uff092\u6b21\u65b9\u7b49\u4e8e\u591a\u5c11x\u7684\u5e73\u65b9\u51cf2xy\u52a0y\u7684\u5e73\u65b9
\u89e3\u6790\uff1a
//\u56e0\u5f0f\u5206\u89e3
91²-(x-y)²
=[91+(x-y)][91-(x-y)]
=-(x-y+91)(x-y-91)
（x-y）²
=x²-2xy+y²
这是平方差公式
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(x-y)²=x²－2xy＋y²
(x-y)²=x²－2xy＋y²，是这样的
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