The quadratic equation whose roots are $l$ and $m$, where $$ \begin{aligned} & l=\lim _{\theta \rightarrow…
The quadratic equation whose roots are $l$ and $m$, where
$$
\begin{aligned}
& l=\lim _{\theta \rightarrow 0}\left(\frac{3 \sin \theta-4 \sin ^2 \theta}{\theta}\right), \\
& m=\lim _{\theta \rightarrow 0} \frac{2 \tan \theta}{\theta\left(1-\tan ^2 \theta\right)}, \text { is }
\end{aligned}
$$
- $x^2+5 x+6=0$
- $x^2-5 x+6=0$
- $x^2-5 x-6=0$
- $x^2+5 x-6=0$
Solution
We have,
$
l=\lim _{\theta \rightarrow 0}\left[\frac{3 \sin \theta-4 \sin ^2 \theta}{\theta}\right]
$
Using $L$-hospital's rule
$
=\lim _{\theta \rightarrow 0} \frac{3 \cos \theta-8 \sin \theta \cos \theta}{1}=3
$
and
$
\begin{aligned}
m & =\lim _{\theta \rightarrow 0} \frac{2 \tan \theta}{\theta\left(1-\tan ^2 \theta\right)} \\
& =\lim _{\theta \rightarrow 0} \frac{\tan 2 \theta}{\theta} \\
& =\lim _{\theta \rightarrow 0} \frac{\tan 2 \theta}{2 \theta} \cdot 2=2
\end{aligned}
$
The required quadratic equation is
$
\begin{aligned}
& x^2-(l+m) x+l m=0 \\
& \Rightarrow \quad x^2-(3+2) x+3 \cdot 2=0 \\
& x^2-5 x+6=0 \\
&
\end{aligned}
$
Asked in: AP EAMCET 2002
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