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If one diagonal of a square is along the line 8x – 15y = 0 and one of its vertex is at (1, 2), then find the equation of sides of the square passing through this vertex.

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Question

If one diagonal of a square is along the line 8x – 15y = 0 and one of its vertex is at (1, 2), then find the equation of sides of the square passing through this vertex.

Sum
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Solution

Let ABCD be the given square and the coordinates of the vertex D be (1, 2).

We are required to find the equations of its sides DC and AD.

Given that BD is along the line 8x – 15y = 0, so its slope is `8/15` (Why?).

The angles made by BD with sides AD and DC is 45° (Why?).

Let the slope of DC be m.

Then tan 45° = `(m - 8/15)/(1 + (8m)/15)`  (Why?)

or 15 + 8m = 15m – 8

or 7m = 23, which gives m = `23/7`

Therefore, the equation of the side DC is given by

y – 2 = `23/7 (x - 1)` or 23x – 7y – 9 = 0.

Similarly, the equation of another side AD is given by

y – 2 = `(-7)/23 (x - 1)` or 7x + 23y – 53 = 0.

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Chapter 10: Straight Lines - Solved Examples [Page 173]

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NCERT Exemplar Mathematics [English] Class 11
Chapter 10 Straight Lines
Solved Examples | Q 11 | Page 173

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