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Question 11 Mark
If $f(2)=4, f^{\prime}(2)=1$, then find $\lim _{x \rightarrow 2}\left[\frac{x f(2)-2 f(x)}{x-2}\right]$
Answer
$ \lim _{x \rightarrow 2} \frac{x f(2)-2 f(x)}{x-2}$
$=\lim _{x \rightarrow 2} \frac{f(2)-2 f^{\prime}(x)}{1} \quad \ldots[\text { By L'Hospital Rule] }$
$=f(2)-2 f^{\prime}(2)$
$=4-2(1)=2 $
[By L' Hospital Rule]
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Question 61 Mark
Differentiate the following w.r.t. x :

$y=\sqrt{ } x+\tan x-x^3$

Answer
$y=\sqrt{x}+\tan x-x^3$
Differentiating w.r.t. $x$, we get
$\begin{aligned}
\frac{ d y}{ d x} & =\frac{ d }{ d x}\left(\sqrt{x}+\tan x-x^3\right) \\
\frac{ d y}{ d x} & =\frac{ d }{ d x}(\sqrt{x})+\frac{ d }{ d x}(\tan x)-\frac{ d }{ d x}\left(x^3\right) \\
& =\frac{1}{2 \sqrt{x}}+\sec ^2 x-3 x^2
\end{aligned}$
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Question 71 Mark
Differentiate the following w.r.t. x :

$y =x^{\frac{4}{3}}+e^x-\sin x$

Answer
$
y=x^{\frac{4}{3}}+ e ^x-\sin x
$
Differentiating w.r.t. $x$, we get
$
\begin{aligned}
\frac{ d y}{ d x} & =\frac{ d }{ d x}\left(x^{\frac{4}{3}}+ e ^x-\sin x\right) \\
\frac{ d y}{ d x} & =\frac{ d }{ d x}\left(x^{\frac{4}{3}}\right)+\frac{ d }{ d x}\left( e ^x\right)-\frac{ d }{ d x}(\sin x) \\
& =\frac{4}{3} x^{\frac{4}{3}-1}+ e ^x-\cos x \\
& =\frac{4}{3} x^{\frac{1}{3}}+ e ^x-\cos x
\end{aligned}
$
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