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If the point A(2, – 4) is equidistant from P(3, 8) and Q(–10, y), find the values of y. Also find distance PQ.

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प्रश्न

If the point A(2, – 4) is equidistant from P(3, 8) and Q(–10, y), find the values of y. Also find distance PQ.

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उत्तर

Given points are A(2, – 4), P(3, 8) and Q(–10, y)

According to the question,

PA = QA

`sqrt((2 - 3)^2 + (-4 - 8)^2) = sqrt((2 + 10)^2 + (-4 - y)^2)`

`sqrt((-1)^2 + (-12)^2) = sqrt((12)^2 + (4 + y)^2)`

`sqrt(1 + 144) = sqrt(144 + 16 + y^2 + 8y)`

`sqrt(145) = sqrt(160 + y^2 + 8y)`

On squaring both sides, we get

145 = 160 + y2 + 8y

y2 + 8y + 160 – 145 = 0

y2 + 8y + 15 = 0

y2 + 5y + 3y + 15 = 0

y(y + 5) + 3(y + 5) = 0

⇒ (y + 5)(y + 3) = 0

⇒ y + 5 = 0

⇒ y = –5

And y + 3 = 0

⇒ y = –3

∴ y = – 3, – 5

Now, PQ = `sqrt((-10 - 3)^2 + (y - 8)^2`

For y = – 3 

PQ = `sqrt((-13)^2 + (-3 - 8)^2`

= `sqrt(169 + 121)`

= `sqrt(290)` units

And for y = – 5 

PQ = `sqrt((-13)^2 + (-5 - 8)^2`

= `sqrt(169 + 169)`

= `sqrt(338)` units

Hence, values of y are – 3 and – 5, PQ = `sqrt(290)` and `sqrt(338)`

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अध्याय 7: Coordinate Geometry - Exercise 7.3 [पृष्ठ ८४]

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एनसीईआरटी एक्झांप्लर Mathematics Exemplar [English] Class 10
अध्याय 7 Coordinate Geometry
Exercise 7.3 | Q 8 | पृष्ठ ८४

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Case Study

Trigonometry in the form of triangulation forms the basis of navigation, whether it is by land, sea or air. GPS a radio navigation system helps to locate our position on earth with the help of satellites.
A guard, stationed at the top of a 240 m tower, observed an unidentified boat coming towards it. A clinometer or inclinometer is an instrument used for measuring angles or slopes(tilt). The guard used the clinometer to measure the angle of depression of the boat coming towards the lighthouse and found it to be 30°.

  1. Make a labelled figure on the basis of the given information and calculate the distance of the boat from the foot of the observation tower.
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