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TS EAMCET · Maths · Straight Lines

If the angle between the pair of lines given by the equation \(a x^2+4 x y+2 y^2=0\) is \(45^{\circ}\) then the possible values of \(a\)

  1. A are -3 or 21
  2. B are \(-6 \pm 4 \sqrt{3}\)
  3. C are \(-6 \pm 24 \sqrt{2}\)
  4. D do not exist
Verified Solution

Answer & Solution

Correct Answer

(B) are \(-6 \pm 4 \sqrt{3}\)

Step-by-step Solution

Detailed explanation

\begin{aligned} & \tan ^{-1}\left(\frac{2 \sqrt{h^2-a b}}{a+b}\right)=45^{\circ} \Rightarrow \tan 45^{\circ}=\frac{2 \sqrt{4-2 a}}{a+2}=1 \\ \Rightarrow & 4(4-2 a)=a^2+4+4 a \Rightarrow a^2+12 a-12=0 \\ \Rightarrow & a=\frac{-12 \pm \sqrt{144+48}}{2}=-6 \pm 4 \sqrt{3}…