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Find the Slope of a Line (I) Which Bisects the First Quadrant Angle (Ii) Which Makes an Angle of 30° with the Positive Direction of Y-axis Measured Anticlockwise.

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Question

Find the slope of a line (i) which bisects the first quadrant angle (ii) which makes an angle of 30° with the positive direction of y-axis measured anticlockwise.

Answer in Brief
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Solution

(i)  We know that the angle between the coordinate axes is \[\frac{\pi}{2}\] .

The line bisects the first quadrant angle.
Inclination of the line with the positive x-axis = \[\frac{1}{2}\left( \frac{\pi}{2} \right) = \frac{\pi}{4}\]

\[\therefore \text { Slope of the line } = \tan\left( \frac{\pi}{4} \right) = 1\]

(ii) The line makes an angle of \[{30}^\circ\] with the positive direction of the y-axis measured anticlockwise

Since the line makes an angle of \[{30}^\circ\]  with the positive direction of the y-axis measured anticlockwise, it makes an angle of \[{90}^\circ + {30}^\circ = {120}^\circ\] with the positive direction of the x-axis measured anticlockwise.

\[\therefore \text { Slope of the line } = \tan {120}^\circ = - \tan {60}^\circ = - \sqrt{3}\]

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Chapter 23: The straight lines - Exercise 23.1 [Page 13]

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R.D. Sharma Mathematics [English] Class 11
Chapter 23 The straight lines
Exercise 23.1 | Q 4 | Page 13

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