\(3^{x+1}+3^{x+3}=810\\ 3^{x+1}\left(1+3^2\right)=810\\ 3^{x+1}\cdot10=810\\ 3^{x+1}=81\\ 3^{x+1}=3^4\\ x+1=4\\ x=3\)
Ta có:
\(3^{x+1}+3^{x+3}=810\)
\(\Rightarrow3^{x+1}.1+3^{x+1}.3^2=810\)
\(\Rightarrow3^{x+1}.\left(1+3^2\right)=810\)
\(\Rightarrow3^{x+1}.10=810\)
\(\Rightarrow3^{x+1}=810:10=81=3^4\)
\(\Rightarrow x+1=4\)
\(\Rightarrow x=3\)
\(3^{x+1}+3^{x+3}=810\)
=>\(3^{x+1}.1+3^2.3^{x+1}=810\)
=>\(3^{x+1}.\left(1+9\right)=810\)
=>\(3^{x+1}.10=810\)
=>\(3^{x+1}=810:10\)
=>\(3^{x+1}=81\)=\(3^4\)
=>\(x+1=4\)
=>\(x=3\)
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