已知A=2x+y,B=2x-y,計算A2-B2.

已知A=2x+y,B=2x-y,計算A2-B2.

A2-B2=(2x+y)2-(2x-y)2=(4x2+4xy+y2)-(4x2-4xy+y2)=4x2+4xy+y2-4x2+4xy-y2=8xy.