若ab=1,求1/(1+a平方)=1/(1+b平方)的值

中间应该是“+”号吧.
1/(1+a^2)+1/(1+b^2)
=ab/(ab+a^2)+ab/(ab+b^2)
=ab/[a(a+b)]+ab/[b(a+b)]
=b/(a+b)+a/(a+b)
=(a+b)/(a+b)
=1