Question

Find the Domain of the following exponential and logarithmic equations and solve them:

Answer 1

The base of a logarithm should always be positive and can't be equal to 1, so the domain is 0 < x < 1 or x > 1.

$\log_{\frac1x}243=5$

Write both sides as powers of 1/x :

$\left(\dfrac1x\right)^{\log_{\frac1x}243}=\left(\dfrac1x\right)^5$

Recall that $a^{\log_ab}=b$, so that

$243=\left(\dfrac1x\right)^5$

$243=\dfrac1{x^5}$

$x^5=\dfrac1{243}$

Take the 5th root of both sides, recalling that 3⁵ = 243, so

$x=\sqrt[5]{\dfrac1{243}}=\boxed{\dfrac13}$