मराठी

If sum of the perpendicular distances of a variable point P (x, y) from the lines x + y – 5 = 0 and 3x – 2y+ 7 = 0 is always 10. Show that P must move on a line.

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प्रश्न

If sum of the perpendicular distances of a variable point P (x, y) from the lines x + y – 5 = 0 and 3x – 2y+ 7 = 0 is always 10. Show that P must move on a line.

बेरीज
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उत्तर

The equations of the given lines are

x + y – 5 = 0      … (1)

3x – 2y + 7 = 0    … (2)

The perpendicular distances of P (x, y) from lines (1) and (2) are respectively given by

`d_1 = |x + y - 5|/(sqrt((1)^2 + (1)^2)` and `d_2 = |3x - 2y + 7|/(sqrt((3)^2 + (2)^2)`

i.e., `d_1 = (x + y - 5)/sqrt2` and `d_2 = |3x -2y + 7|/sqrt(13)`

It is given that d1 + d2 = 10

`= (x + y - 5)/sqrt2 + |3x -2y + 7|/sqrt(13) = 10`

= `sqrt13 |x + y - 5| + sqrt2 |3x -2y + 7|-10sqrt26 = 0`

= `sqrt13 |x + y - 5| + sqrt2 |3x -2y + 7|-10sqrt26 = 0`

[Assuming (x + y - 5) and (3x - 2y + 7) are positive]

= `sqrt13x + sqrt13y - 5sqrt13 + 3sqrt2x - 2sqrt2y + 7sqrt2 - 10sqrt26 = 0`

= `x(sqrt13x + 3sqrt2) + y (sqrt13 - 2sqrt2) + (7sqrt2 - 5sqrt13 - 10sqrt26) = 0` which is the equation of a line.

Similarly, we can obtain the equation of line for any signs of (x + y -5) and (3x - 2y + 7)

Thus, point P must move on a line.

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पाठ 9: Straight Lines - Miscellaneous Exercise [पृष्ठ १७३]

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एनसीईआरटी Mathematics [English] Class 11
पाठ 9 Straight Lines
Miscellaneous Exercise | Q 19. | पृष्ठ १७३

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