X²+Y²=(X+Y)²-2XY為什麼?
回答 (3)
✔ 最佳答案
x^2 +y^2
=x^2+2xy+y^2 -2xy
=(x+y)^2-2xy
(x+y)^2=x^2+y^2+2xy
(x+y)^2-2xy=x^2+y^2
因為 (X+Y)²=X²+2XY+Y²,所以 (X+Y)²-2XY = (X²+2XY+Y²)-2XY = X²+Y² ,得證 X²+Y² = (X+Y)²-2XY
收錄日期: 2021-04-18 14:41:41
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