If the slopes of the lines $\mathrm{Kx}^2-4 \mathrm{xy}+5 \mathrm{y}^2=0$ differ by 2 , then $\mathrm{K}=$

If the slopes of the lines $\mathrm{Kx}^2-4 \mathrm{xy}+5 \mathrm{y}^2=0$ differ by 2 , then $\mathrm{K}=$
  1. $\frac{-21}{5}$
  2. $\frac{21}{5}$
  3. $\frac{5}{21}$
  4. $\frac{4}{5}$

Solution

$\begin{aligned} & \left|m_1-m_2\right|=\sqrt{\left(m_1+m_2\right)^2-4 m_1 m_2}=\frac{2 \sqrt{h^2-a b}}{b} \\ & \Rightarrow 2=\frac{2 \sqrt{(-2)^2-\mathrm{K} \times 5}}{5} \\ & \Rightarrow 5=\sqrt{4-5 K} \\ & \Rightarrow 25=4-5 \mathrm{~K} \\ & \Rightarrow \mathrm{K}=\frac{-21}{5}\end{aligned}$

Asked in: MHT CET 2022 (05 Aug Shift 2)

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