恒等式计算判断X^2 - Y^2 -(X - Y)^2 =2Y(X - Y)是否恒等式请清楚写明步骤!

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恒等式计算判断X^2 - Y^2 -(X - Y)^2 =2Y(X - Y)是否恒等式请清楚写明步骤!

恒等式计算判断X^2 - Y^2 -(X - Y)^2 =2Y(X - Y)是否恒等式请清楚写明步骤!
恒等式计算
判断X^2 - Y^2 -(X - Y)^2 =2Y(X - Y)是否恒等式
请清楚写明步骤!

恒等式计算判断X^2 - Y^2 -(X - Y)^2 =2Y(X - Y)是否恒等式请清楚写明步骤!
X^2 - Y^2 -(X - Y)^2
=X^2 - Y^2 -(X^2 - 2XY+Y^2)
=2XY-2Y^2
=2Y(X-Y)
所以是恒等式

X~2-Y~2-X~2+2XY-Y~2=2YX-2Y~2=2Y(X-Y)
恒等式