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A Straight Line is Drawn Cutting Two Equal Circles and Passing Through the Mid-point M of the Line Joining Their Centers O and O'. Prove that the Chords Ab and Cd - Mathematics

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प्रश्न

A straight line is drawn cutting two equal circles and passing through the mid-point M of the line joining their centers O and O'. Prove that the chords AB and CD, which are intercepted by the two circles, are equal.

योग

उत्तर


Given: A straight line AD intersects two circles of equal radii at A, B, C and D.
The line joining the centers OO' intersect AD at M and M is the midpoint of OO'.

To Prove: AB = CD.

Construction: From O, draw OP ⊥ AB and from O', draw O'Q ⊥ CD.

Proof:  
In ΔOMP and ΔO'MQ,
∠OMP = ∠O'MQ            ...( Vertically Opposite angles )
∠OPM = ∠O'QM            ...( each = 90° ) 
OM = O'M                      ...( Given )

By Angle-Angle-Side criterion of congruence,
∴ ΔOMP ≅ ΔO'MQ,       ...( by AAS )

The corresponding parts of the congruent triangles are congruent.
∴ OP = O'Q                     ...( c.p.c.t. )

We know that two chords of a circle or equal circles which are equidistant from the center are equal.
∴ AB = CD.

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अध्याय 17: Circle - Exercise 17 (B) [पृष्ठ २१७]

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सेलिना Concise Mathematics [English] Class 9 ICSE
अध्याय 17 Circle
Exercise 17 (B) | Q 2 | पृष्ठ २१७
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