The slope of a line is double of the slope of another line. If tangent of the angle between them is 1/3, find the slopes of the lines.
The slope of a line is double of the slope of another line. If tangent of the angle between them is 1/3, find the slopes of the lines.

Allow us to consider ‘m1’ and ‘m’ be the incline of the two given lines to such an extent that

    \[\mathbf{m1}\text{ }=\text{ }\mathbf{2m}\]

We realize that in case θ is the point somewhere within l1 and l2 with incline m1 and m2, then, at that point,

NCERT Solutions for Class 11 Maths Chapter 10 – Straight Lines image - 10

    \[\mathbf{1}+\mathbf{2m2}\text{ }=\text{ }-\text{ }\mathbf{3m}\]

    \[\mathbf{2m2}\text{ }+\mathbf{1}\text{ }+\mathbf{3m}\text{ }=\text{ }\mathbf{0}\]

    \[\mathbf{2m}\text{ }\left( \mathbf{m}+\mathbf{1} \right)\text{ }+\text{ }\mathbf{1}\left( \mathbf{m}+\mathbf{1} \right)\text{ }=\text{ }\mathbf{0}\]

    \[\left( \mathbf{2m}+\mathbf{1} \right)\text{ }\left( \mathbf{m}+\mathbf{1} \right)=\text{ }\mathbf{0}\]

    \[\mathbf{m}\text{ }=\text{ }-\text{ }\mathbf{1}\text{ }\mathbf{or}\text{ }-\text{ }\mathbf{1}/\mathbf{2}\]

In the event that

    \[\mathbf{m}\text{ }=\text{ }-\text{ }\mathbf{1}\]

, the incline of the lines are

    \[-\text{ }\mathbf{1}\text{ }\mathbf{and}\text{ }-\text{ }\mathbf{2}\]

In the event that

    \[\mathbf{m}\text{ }=\text{ }-\text{ }\mathbf{1}/\mathbf{2}\]

, the incline of the lines are

    \[-\text{ }\mathbf{1}/\mathbf{2}\text{ }\mathbf{and}\text{ }-\text{ }\mathbf{1}\]

Case 2:

NCERT Solutions for Class 11 Maths Chapter 10 – Straight Lines image - 11

    \[\mathbf{2m2}\text{ }\text{ }\mathbf{3m}\text{ }+\text{ }\mathbf{1}\text{ }=\text{ }\mathbf{0}\]

    \[\mathbf{2m2}\text{ }\text{ }\mathbf{2m}\text{ }\text{ }\mathbf{m}\text{ }+\text{ }\mathbf{1}\text{ }=\text{ }\mathbf{0}\]

    \[\mathbf{2m}\text{ }\left( \mathbf{m}\text{ }\text{ }\mathbf{1} \right)\text{ }\text{ }\mathbf{1}\left( \mathbf{m}\text{ }\text{ }\mathbf{1} \right)\text{ }=\text{ }\mathbf{0}\]

    \[\mathbf{m}\text{ }=\text{ }\mathbf{1}\text{ }\mathbf{or}\text{ }\mathbf{1}/\mathbf{2}\]

In the event that

    \[\mathbf{m}\text{ }=\text{ }\mathbf{1}\]

, the incline of the lines are 1 and 2

 

In the event that

    \[\mathbf{m}\text{ }=\text{ }\mathbf{1}/\mathbf{2}\]

, the incline of the lines are 1/2 and 1

 

The incline of the lines are

    \[\left[ -\mathbf{1}\text{ }\mathbf{and}\text{ }-\text{ }\mathbf{2} \right]\text{ }\mathbf{or}\text{ }\left[ -\mathbf{1}/\mathbf{2}\text{ }\mathbf{and}\text{ }-\text{ }\mathbf{1} \right]\text{ }\mathbf{or}\text{ }\left[ \mathbf{1}\text{ }\mathbf{and}\text{ }\mathbf{2} \right]\text{ }\mathbf{or}\text{ }\left[ \mathbf{1}/\mathbf{2}\text{ }\mathbf{and}\text{ }\mathbf{1} \right]\]