If the pairs of straight lines \(x^2-2 q x y-y^2=0\) and \(x^2-2 p x y-y^2=0\) bisect the angles between…

If the pairs of straight lines \(x^2-2 q x y-y^2=0\) and \(x^2-2 p x y-y^2=0\) bisect the angles between each other, then which of the following is correct?
  1. \(1-p q=0\)
  2. \(p q-1=0\)
  3. \(p q+1=0\)
  4. \(p q=0\)

Solution

It is given that the pair of straight lines \(x^2-2 p x y-y^2=0\) and \(x^2-2 q x y-y^2=0\) bisect, the angles between each other, then equations \(\frac{x^2-y^2}{1-(-1)}=\frac{x y}{-p}\) and \(x^2-2 q x y-y^2=0\) represents same line, so \(x^2+\frac{2}{p} x y-y^2=0\) represents \(x^2-2 q x y-y^2=0\) on comparing, we get \(\frac{2}{p}=-2 q\) \(\Rightarrow \quad p q+1=0\) Hence, option (c) is correct.

Asked in: AP EAMCET 2020 (21 Sep Shift 2)

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