化简计算3(x+y)²-2(x-2y)²

更新时间：2021-06-15 06:54:37 200次访问

   3﹙x＋y﹚²－2﹙x－2y﹚²

＝3x²＋6xy＋3y²－2﹙x²－4xy＋4y²﹚

＝3x²＋6xy＋3y²－2x²＋8xy－8y²

＝x²＋14xy－5y²

3(x+y)²-2(x-2y)²

=3(x²+2xy+y²)-2(x²-4xy+4y²)

=3x²+6xy+3y²-2x²+8xy-8y²

=(3x²-2x²)+(6xy+8xy)+(3y²-8y²)

=x²+14xy-5y²

3(x+y)²-2(x-2y)²

=3(x²+2xy+y²)-2(x²-4xy+4y²)

=3x²+6xy+3y²-2x²+8xy-8y²

=x²+14xy-5y²