下列等式成立的是( ) A.x2+y2=(x+y)(x+y) B.x2-y2=( 发布时间:2017-05-13 13:44 │ 来源:www.tikuol.com 题型:选择题 问题: 下列等式成立的是( )A.x2+y2=(x+y)(x+y)B.x2-y2=(x+y)(x-y)C.-x2+y2=(-x+y)(-x-y)D.-x2-y2=-(x+y)(x-y)