[tex]\it 2.\ 7^1\cdot7^2\cdot7^3\cdot\ ...\ \cdot7^50=7^{1+2+3+\ ...\ +50}=7^{\dfrac{50\cdot51}{2}}=7^{51\cdot25}=7^{1275}\\ \\ Egalitatea\ din\ enun\c{\it t}\ devine:\ 7^{1275}=7^x \Rightarrow x=1275.[/tex]
3.
[tex]\it a=5^0+5^1+5^2+5^3+\ ...\ +5^{2016}+5^{2017} \Longrightarrow\\ \\ \Longrightarrow a=(1+5)+5^2(1+5)+\ ...\ +5^{2016}(1+5) =6(1+5^2+\ ...\ +5^{2016})\Longrightarrow\\ \\ \Longrightarrow a\ \vdots\ 6[/tex]
