X平方+Y的平方;可以化为什么?跟分解因式有关的。!
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X平方-Y的平方=(X+Y)(X-Y)
X^2+Y^2=-(X^2-Y^2)=-(X+Y)(X-Y)
得(x+y)的平方-2xy或者(x-y)的平方+2xy
如上（x+y)^2-2xy或（x-y)^2+2xy
X平方+Y的平方=(X+Y)的平方-2XY
绛旓細濡傛灉鏄+鍙凤紝閭ｄ箞x²+y²涓嶈兘鍒嗚В 濡傛灉涓棿鏄-鍙凤紝閭ｄ箞鍙互鍒嗚В x²-y²=(x+y)(x-y)
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绛旓細鏈涢噰绾筹綖
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绛旓細x鐨勫钩鏂+y鐨勫钩鏂锛歺²+y²=锛坸+y锛²-2xy 锛1锛夎繖鏄敱瀹屽叏骞虫柟鍏紡杞崲鏉ョ殑锛氾紙x+y锛²=x²+2xy+y²锛2锛夊垎鏋愯繃绋嬪涓嬶細锛坸+y锛²-2xy =锛坸+y锛*锛坸+y锛-2xy =x²+y²+2xy-2xy =x²+y²...
