Ta có: \(2^m+2^n=2^{m+n}\)
<=>\(2^m+2^n=2^m.2^n\)
<=>\(1+2^n-1=2^m\left(2^n-1\right)\)
<=>\(\left(2^m-1\right)\left(2^n-1\right)=1\)
Do m,n là số tự nhiên =>\(\hept{\begin{cases}2^m-1=1\\2^n-1=1\end{cases}}\)<=>\(\hept{\begin{cases}2^m=2\\2^n=2\end{cases}}\)<=>\(\hept{\begin{cases}m=1\\n=1\end{cases}}\)