Number of solutions of equation $\log_2 (9-2^x)=10^{\log_{10}(3-x)}$, is _______.
Answer & explanation
We have,
$\log_2 (9-2^x)=10^{\log_{10}(3-x)}$
$⇒ \log_2 (9-2^x)=(3-x)$ $[∵a^{\log_a\, N}=N]$
$⇒(9-2^x)=2^{(3-x)}$
$⇒(9-2^x)=2^3×2^{-x}$
$⇒9.2^x-(2^x)2=8$
$⇒(2^x)^2-9.2^x+8=0$
$⇒(2^x-8) (2^x-1)=0$
$⇒2^x = 2^3$ or, $2^x = 2^0⇒ x=3$ or, $x=0$
Also, the given equation exists for
$9-2^x>0$ and $3-x>0$
i.e. for $2^x <9$ and $x < 3$
i.e. for $x <\log_2 9$ and $x < 3$.
Hence, x = 0 is the only solution of the given equation.