The acute angle between the lines $x \cos 30^{\circ}+y \sin 30^{\circ}=3$ and $x \cos 60^{\circ}+y \sin…

The acute angle between the lines $x \cos 30^{\circ}+y \sin 30^{\circ}=3$ and $x \cos 60^{\circ}+y \sin 60^{\circ}=5$ is
  1. $75^{\circ}$
  2. $30^{\circ}$
  3. $60^{\circ}$
  4. $45^{\circ}$

Solution

Given equations of lines, $x \cos 30^{\circ}+y \sin 30^{\circ}=3$ and $x \cos 60^{\circ}+y \sin 60^{\circ}=5$ $\Rightarrow \sqrt{3} x+y=6$ and $x+\sqrt{3} y=10$ $\therefore \quad$ Slope of line $\sqrt{3} x+y=6=m_1=-\sqrt{3}$ Slope of line $x+\sqrt{3} y=10=\mathrm{m}_2=\frac{-1}{\sqrt{3}}$ $\begin{aligned} \therefore \quad \tan \theta & =\left|\frac{m_1-m_2}{1+m_1 m_2}\right| \\ & =\left|\frac{-\sqrt{3}+\frac{1}{\sqrt{3}}}{1+(-\sqrt{3}) \times\left(\frac{-1}{\sqrt{3}}\right)}\right| \\ & =\left|\frac{-3+1}{2 \sqrt{3}}\right| \\ & =\left|\frac{-2}{2 \sqrt{3}}\right| \\ \therefore \quad \tan \theta & =\frac{1}{\sqrt{3}} \\ \therefore \quad \Rightarrow \theta & =30^{\circ}\end{aligned}$

Asked in: MHT CET 2024 (04 May Shift 2)

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