如果a:b=c:d,mb+nd不等于0,问(ma+nc)/(mb+nd)是否与a/b相等?

问题描述:

如果a:b=c:d,mb+nd不等于0,问(ma+nc)/(mb+nd)是否与a/b相等?

相等
设a/b=c/d=k,则a=bk,c=dk
(ma+nc)/(mb+nd)=(mbk+ndk)/(mb+nd)=k(mb+nd)/(mb+nd)=k
所以,a/b=(ma+nc)/(mb+nd)