Test Index

NCERT Class XI Mathematics - Straight Lines - Solutions

© examsnet.com
Question : 46 of 74
Marks: +1, -0
Two lines passing through the point (2, 3) intersects each other at an angle of 60°. If slope of one line is 2, find equation of the other line.
Solution:  
We have given a point (2, 3), through which two lines are passing and intersects at an angle of 60°.
Let m be the slope of the other line
⇒ tan 60° = m21+2m\left|\frac{m-2}{1+2m}\right| ⇒ ± 3\sqrt{3} = m21+2m\frac{m-2}{1+2m}
3\sqrt{3} = m21+2m\frac{m-2}{1+2m} ... (i)
or - 3\sqrt{3} = m21+2m\frac{m-2}{1+2m} ... (ii)
3+23m\sqrt{3}+2\sqrt{3}m = m - 2 or 3+23m\sqrt{3}+2\sqrt{3}m = 2 - m
3\sqrt{3} + 2 = m - 232\sqrt{3} m or 232\sqrt{3} m + m = 2 - 3\sqrt{3}
⇒ m = 3+2123\frac{\sqrt{3}+2}{1-2\sqrt{3}} or m = 231+23\frac{2-\sqrt{3}}{1+2\sqrt{3}}
Since the line passes through (2, 3)
∴ Its equation is either
y - 3 = 3+2123(x2)\frac{\sqrt{3}+2}{1-2\sqrt{3}} (x-2) ... (iii)
or y - 3 = 231+23(x2)\frac{2-\sqrt{3}}{1+2\sqrt{3}} (x-2) ... (iv)
(iii) ⇒ (y − 3)(1 − 23\sqrt{3}) = (3\sqrt{3} + 2) (x − 2)
⇒ y (1 − 23\sqrt{3}) − 3(1 − 23\sqrt{3}) = (3\sqrt{3} + 2)x − 2(3\sqrt{3} + 2)
⇒ y (1 − 23\sqrt{3}) − (3 − 6 3\sqrt{3}) = (3\sqrt{3} + 2)x − 2 3\sqrt{3} −4
⇒ 2 3\sqrt{3} + 4 − 3 + 6 3\sqrt{3} =(3\sqrt{3} + 2)x +(23\sqrt{3} − 1)y
⇒(3\sqrt{3} + 2)x + (23\sqrt{3} − 1)y− 8 3\sqrt{3} − 1 = 0 ... (v)
And
(iv) ⇒ (y − 3) (1 + 23\sqrt{3}) = (2 − 3\sqrt{3}) (x −2)
⇒ y(1 + 23\sqrt{3}) − 3 (1 + 23\sqrt{3}) = (2 − 3\sqrt{3})x − 2(2 − 3\sqrt{3})
⇒ − 3 − 6 3\sqrt{3} + 2(2 − 3\sqrt{3}) = (2 − 3\sqrt{3})x− y(1+ 2 3\sqrt{3})
⇒ − 3 − 6 3\sqrt{3} +4 − 2 3\sqrt{3} =(2 − 3\sqrt{3})x − y (1 + 2 3\sqrt{3})
⇒ (2 − 3\sqrt{3})x −(1 + 2 3\sqrt{3})y + 83√3 − 1 = 0 ... (vi)
Thus (v) and (vi) are the required equations of the line.
© examsnet.com
Go to Question: