计算:(﹣x﹣y)(x﹣y)+(x+y)2
解:(﹣x﹣y)(x﹣y)+(x+y)2,
=(﹣y)2﹣x2+(x+y)2,
=﹣x2+y2+x2+2xy+y2,
=2y2+2xy.
心肺复苏操作目的?