Question

\(\left(-7\right)^x=\frac{1}{49}\)

\(\left(-2\right)^x=-0,125\)

Answer 1

\(\left(-7\right)^x=\frac{1}{49}\)

\(\left(-7\right)^x=\left(-7\right)^{-2}\)

\(x=-2\)

\(\left(-2\right)^x=-0,125\)

\(\left(-2\right)^x=\left(-2\right)^{-3}\)

\(x=-3\)

Answer 2

\(\left(-7\right)^x=\frac{1}{49}\Rightarrow x< 0\Rightarrow\frac{1}{\left(-7\right)^{-x}}=\frac{1}{49}\Rightarrow x=-2\) 

\(\left(-2\right)^x=-0,125=-\frac{1}{8}\Rightarrow x< 0\Rightarrow\frac{1}{\left(-2\right)^{-x}}=-\frac{1}{8}\) mà \(\left(-2\right)^{-x}\ge0\Rightarrow\) k tồn tại x