Học dốt giúp dc ko =))))))
Bài 1 :
a, \(x^{15}=x\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)
Vậy .....
b, \(\left(2x+1\right)^3=125\)
\(\Leftrightarrow\left(2x+1\right)^3=5^3\)
\(\Leftrightarrow2x+1=5\)
\(\Leftrightarrow2x=4\)
\(\Leftrightarrow x=2\)
Vậy .....
c, \(\left(x-5\right)^4=\left(x-5\right)^6\)
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x-5=1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=5\\x=6\end{matrix}\right.\)
\(A=3+3^2+3^3+...+3^{100}\)
\(3A=3\left(3+3^2+3^3+...+3^{100}\right)\)
\(3A=3^2+3^3+3^4+...+3^{101}\)
\(3A-A=\left(3^2+3^3+3^4+...+3^{101}\right)-\left(3+3^2+3^3+...+3^{100}\right)\)
\(2A=3^{101}-3\)
\(2A+3=3^{101}=3^n\)
\(n=101\)
