[tex]\displaystyle \bf \\
2^n+2^{n+2}+2^{n+1} =56\\\\
2^n+2^{n}\times 2^{2}+2^{n}\times 2^{1} =56\\\\
\text{\bf \^Il dam factor comun pe }~2^n\\\\
2^n(1+2^2+2^1)=56\\\\
2^n(1+4+2)=56\\\\
7\times 2^n = 56\\\\
2^n = \frac{56}{7} \\\\
2^n = 8\\\\
2^n = 2^3\\\\
\boxed{\bf n = 3}
[/tex]
