Find the value of \(k\), if the angle between the straight lines represented by \(2 x^2+5 x y+3 y^2+6 x+7…

Find the value of \(k\), if the angle between the straight lines represented by \(2 x^2+5 x y+3 y^2+6 x+7 y+4=0\) is \(\tan ^{-1}(k)\).
  1. \(\left(\frac{1}{5}\right)\) only
  2. \(\left(\frac{-1}{5}\right)\) only
  3. \(\pm \frac{1}{5}\)
  4. 0

Solution

Straight lines \(2 x^2+5 x y+3 y^2+6 x+7 y+4=0\) Angle between straight lines represented by \(\begin{aligned} & a x^2+b y^2+2 g x+2 f y+c+2 h x y=0 \text { is } \\ & \tan \theta=\frac{2 \sqrt{h^2-a b}}{a+b} \end{aligned}\) \(\begin{aligned} \tan \theta & =\frac{2 \sqrt{(5 / 2)^2-6}}{5}= \pm \frac{1}{5} \\ \Rightarrow \quad \theta & =\tan ^{-1} K=\tan ^{-1}\left( \pm \frac{1}{5}\right) \Rightarrow\left(K= \pm \frac{1}{5}\right) \end{aligned}\)

Asked in: AP EAMCET 2020 (17 Sep Shift 1)

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