NCERT Class XI Mathematics - Straight Lines - Solutions

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Question : 68
Total: 74
Find the distance of the line 4x + 7y + 5 = 0 from the point (1, 2) along the line 2x – y = 0.
Solution:  

The given equation of line is
2x – y = 0 ... (i)
and the point Q(1, 2) lies on this line.
We also have given
4x + 7y + 5 = 0 ... (ii)
On solving (i) and (ii), we get x =
5
18
, y =
5
9

Thus the lines (i) and (ii) meet at R (
5
18
,
5
9
)

∴ The required distance = |QR|
= (
5
18
1
)
2
+(
5
9
2
)
2

=
529
324
+
529
81
=
529
81
(
1
4
+1
)
=
23
9
5
4
=
235
18
units.
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