मराठी

Two Equal Chords Ab and Cd of a Circle with Center O, Intersect Each Other at Point P Inside the Circle. Prove That: (I) Ap = Cp ; (Ii) Bp = Dp - Mathematics

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प्रश्न

Two equal chords AB and CD of a circle with center O, intersect each other at point P inside the circle.
Prove that: (i) AP = CP ; (ii) BP = DP

बेरीज

उत्तर

Drop OM and ON perpendicular on AB and CD.
Join OP, OB, and OD.

∴ OM and ON bisect AB and CD respectively.     ....( Perpendicular drawn from the centre of a circle to a chord bisects it. )
∴ MB = `1/2"AB" = 1/2"CD" = "ND"`....(i)

In right ΔOMB,
OM2 = OB2 - MB2                            ....(ii)
In right ΔOND,
ON2 = OD2 - ND                          ....(iii)

From (i), (ii), and (iii),
OM = ON

In ΔOPM and ΔOPN,
∠OMP = ∠ONP          ....( both 90° )
OP = OP                     ....( common )
OM = ON                   ....( proved above )
By Right Angle-Hypotenuse-Side criterion of congruence,
∴ ΔOPM ≅ ΔOPN      ....( by RHS )

The corresponding parts of the congruent triangles are congruent.
∴ PM = PN                ....( c.p.c.t. )

Adding (i) to both sides,
MB + PM = ND + PN
⇒ BP = DP
Now, AB = CD
∴  AB - BP = CD - DP     ...( ∵ BP = DP )
⇒ AP = CP.

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

APPEARS IN

सेलिना Concise Mathematics [English] Class 9 ICSE
पाठ 17 Circle
Exercise 17 (B) | Q 5 | पृष्ठ २१७

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