已知（a＋b）＝7，（a-b）＝3求⑴a＋b⑵ab

更新时间2019-04-01 21:39:09

(1)

   a²+b²

=[(a+b)²+(a-b)²]/2

=(7+3)/2

=5

(2) ab

=[(a+b)²-(a-b)²]/4

=(7-3)/4

=1

a=5,b=2.[1]a+b=7,[2]ab=10.

1等于5，2等于1