Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Continuity and Differentiability

Question:

Let $f(x)=(\sin x)^{\frac{1}{π-2x}},\,x≠\frac{π}{2}$. If f (x) is continuous at $x=\frac{π}{2}$, then $f(\frac{π}{2})$ is

Options:

$e$

1

0

none of these

Correct Answer:

1

Explanation:

Here, $\underset{h→0}{\lim}\begin{Bmatrix}\sin\begin{pmatrix}\frac{π}{2}+h\end{pmatrix}\end{Bmatrix}^{\frac{1}{π-2(π/2+h)}}=\underset{h→0}{\lim}\begin{Bmatrix}\sin\begin{pmatrix}\frac{π}{2}-h\end{pmatrix}\end{Bmatrix}^{\frac{1}{π-2(π/2-h)}}=f\begin{pmatrix}\frac{π}{2}\end{pmatrix}$

Now, $\underset{h→0}{\lim}(\cos h)^{\frac{1}{(-2h)}}=e^{\underset{h→0}{\lim}(1/(-2h))\log\cos h}=e^{\underset{h→0}{\lim}\frac{(1/\cos h)(-\sin h)}{2}}=e^0=1$

$∴f\begin{pmatrix}\frac{π}{2}\end{pmatrix}=1$