The solution set of the inequation $\frac{1}{\log_2x}<\frac{1}{\log_2\sqrt{x+2}}$, is
Answer & explanation
Correct answer: option 3
Two sides of the given inequation are defined for $x>0$ and $x ≠ 1$.
Now, two cases arise.
CASE I When $x>1$
In this case, we have
$\log_2x>0$ and $\log_2\sqrt{x+2}>0$
$∴\frac{1}{\log_2x}<\frac{1}{\log_2\sqrt{x+2}}$
$⇒\log_2\sqrt{x+2}<\log_2x$
$⇒\sqrt{x+2}<x$
$⇒x+2<x^2$
$⇒x^2-x-2>0$
$⇒(x-2)(x+1)>0$
$⇒x-2>0$ $[∵x>1⇒x+1>0]$
$⇒x>2⇒x∈(2,∞)$
CASE II When $0<x<1$
In this case, we have
$\log_2x<0$ and $\log_2\sqrt{x+2}>0$
So, the inequation $\frac{1}{\log_2x}<\frac{1}{\log_2\sqrt{x+2}}$ holds for all $x ∈(0, 1)$.
Hence, the solution set of the given inequation is $(0,1) ∪ (2,∞)$.