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Two lines passing through the point (2, 3) intersects each other at an angle of \(60º .\) If slope of one line is 2, find equation of the other line.

Updated On: Jan 22, 2026
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Solution and Explanation

It is given that the slope of the first line, \(m_1 = 2. \)
Let the slope of the other line be \(m_2\)
The angle between the two lines is \(60°.\)

\(∴tan60º=\left|\frac{m_1-m_2}{1+m_1m_2}\right|\)

\(⇒\sqrt3=\left|\frac{2-m_2}{1+2m_2}\right|\)

\(⇒\sqrt3=±\left(\frac{2-m_2}{1+2m_2}\right)\)

\(⇒\sqrt3=\left(\frac{2-m_2}{1+2m_2}\right) or \sqrt3=-\left(\frac{2-m_2}{1+2m_2}\right)\)

\(⇒\sqrt3(1+2m_2)=2-m_2 \space or \sqrt3(1+2m_2)=-(2-m_2)\)
\(⇒\sqrt3+2\sqrt3m_2+m_2=2 \space or \sqrt3+2\sqrt3m_2-m_2=-2\)

\(⇒m_2=\frac{2-\sqrt3}{\left(2\sqrt3+1\right)}\space  or\space m_2=-\frac{\left(2+\sqrt3\right)}{\left(2\sqrt3-1\right)}\)

Case I\(m_2=\frac{2-\sqrt3}{\left(2\sqrt3+1\right)}\)
The equation of the line passing through point (2, 3) and having a slope of\(\frac{\left(2-\sqrt3\right)}{\left(2\sqrt3+1\right)}\) is

\((y-3)=\frac{2-\sqrt3}{2\sqrt3+1}(x-2)\)

\((2\sqrt3+1)(y-3)=(2-\sqrt3)x-2(2-\sqrt3)\)

\((\sqrt3-2)x+(2\sqrt3+1)y=-4+2\sqrt3+6\sqrt3+3\)
\((\sqrt3-2)x+(2\sqrt3+1)y=-1+8\sqrt3\)
In this case, the equation of the other line is \((\sqrt3-2)x+(2\sqrt3+1)y=-1+8\sqrt3\)

Case II\(m_2=\frac{-\left(2+\sqrt3\right)}{\left(2\sqrt3-1\right)}\)
The equation of the line passing through point (2, 3) and having a slope of\( \frac{-\left(2+\sqrt3\right)}{\left(2\sqrt3-1\right)}\) is

\((y-3)=\frac{-\left(2+\sqrt3\right)}{\left(2\sqrt3-1\right)}\left(x-2\right)\)

\((2\sqrt3-1)y-3(2\sqrt3-1)=-(2+\sqrt3)x+2(2+\sqrt3)\)
\((2\sqrt3-1)y+(2+\sqrt3)x=4+2\sqrt3+6\sqrt3-3\)
\((2+\sqrt3)x+(2\sqrt3-1)y=1+8\sqrt3\)

In this case, the equation of the other line is\( (2+\sqrt3)x+(2\sqrt3-1)y=1+8\sqrt3\)

Thus, the required equation of the other line is\( (\sqrt3-2)x+(2\sqrt3+1)y\)\(=-1+8\sqrt3\)  or \( (2+\sqrt3)x+(2\sqrt3-1)y=1+8\sqrt3\)

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