If $ sin^{-1}(sin 5) > x^2 - 4x , $ then
Answer & explanation
Correct answer: option 2
The correct answer is Option 2: $x ∈ ( 2 - \sqrt{9-2\pi}, 2+\sqrt{9-2\pi} )$
We have,
$\sin^{-1}(\sin 5) > x^2 - 4x $
We know:
$\sin^{-1}(\sin θ)=θ$ only if $θ∈\left[-\frac{\pi}{2},\frac{\pi}{2}\right]$
But 5 radians is not in $\left[-\frac{\pi}{2},\frac{\pi}{2}\right]$. So we use:
$\sin^{-1}(\sin 5) =5-2\pi$ (since $5∈[\pi,2\pi]$ and $\sin 5=\sin(2\pi-5)$)
Now the inequality becomes:
$5-2\pi>x^2-4x$
Step 2: Bring all terms to one side:
$⇒ 5 - 2 \pi > x^2 - 4x $
$⇒ x^2 - 4x - 5 + 2 \pi < 0 ⇒2 - \sqrt{9-2 \pi} < x < 2 + \sqrt{9-2 \pi}$