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Maharashtra State BoardSSC (English Medium) 9th Standard

Radius of a circle with centre O is 41 units. Length of a chord PQ is 80 units, find the distance of the chord from the centre of the circle. - Geometry

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Question

Radius of a circle with centre O is 41 units. Length of a chord PQ is 80 units, find the distance of the chord from the centre of the circle.

Sum

Solution

Let O be the center of the circle and seg PQ is its chord.

seg OR ⊥ chord PQ such that, P-R-Q

PQ = 80 unit

OP = 41 unit

PR = `1/2` PQ       ...(Perpendicular drawn from the center of a circle to the chord bisects the chord.)

∴ PR = `1/2 xx 80`

∴ PR = 40 unit

In ∆ORP, From Pythagoras theorem,

OP2 = OR2 + PR2

∴ 412 = OR2 + 402

∴ 1681 = OR2 + 1600

∴ OR2 = 1681 – 1600

∴ OR2 = 81

∴ OR = `sqrt(81)`

∴ OR = 9 unit

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Properties of Chord
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Chapter 6: Circle - Practice Set 6.1 [Page 79]

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