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 $$ \begin{aligned} & l=\lim _{\theta \rightarrow 0}\left(\frac{3 \sin \theta-4 \sin ^2 \theta}{\theta}\right), \\ & m=\lim _{\theta \rightarrow 0} \frac{2 \tan \theta}{\theta\left(1-\tan ^2 \theta\right)}, \text { is } \end{aligned} $$
  1. $x^2+5 x+6=0$
  2. $x^2-5 x+6=0$
  3. $x^2-5 x-6=0$
  4. $x^2+5 x-6=0$

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

Practice more Quadratic Equation questions on Aicharya