Question

Cho mk sửa lại câu b nè 

\(\frac{81}{\left(-3\right)^x}=-243\)

Answer 1

\(\frac{81}{\left(-3\right)^x}=-243\)
\(\frac{81}{\left(-3\right)^x}=\frac{-241}{1}=81.1:-241=\frac{-1}{3}\)

Answer 2

\(\frac{81}{\left(-3\right)^x}=-243\)

\(\left(-3\right)^x=\frac{81}{-243}\)

\(\left(-3\right)^x=-\frac{1}{3}\)

\(\left(-3\right)^x=\left(-3\right)^{-1}\)

\(x=-1\)

Answer 3

\(\frac{81}{\left(-3\right)^x}=-243< =>\frac{81}{-243}=\left(-3\right)^x< =>\frac{1}{-3}=\left(-3\right)^x\)

\(< =>1=\left(-3\right)^x\left(-3\right)< =>1=\left(-3\right)^{x+1}\)

<=> x=-1 vì \(\left(-3\right)^0=1\)