a-b=5
(a-b)^2=25
a^2-2ab+b^2=25
a^2+b^2=25+2ab=25+2*(3/2)=25+3=28
（a+b)平方
=a^2+2ab+b^2
=a^2+b^2+2ab
=28+2*(3/2)
=28+3
=31