Let AB and CD be the two equal chords (AB = CD = a). Let the chords intersect at point P. Join OP.
Draw OM and ON perpendicular to chords AB and CD respectively.

We know that,
Perpendicular from center bisects the chord.
∴ AM = MB = and CN = DN =
Since, AB = CD.
∴ AM = MB = CN = DN = x(let) .....(1)
In ∆ OMP and ∆ ONP,
⇒ ∠M = ∠N (Both equal to 90°)
⇒ OP = OP (Common side)
⇒ OM = ON (Equal chords are equidistant from the center.)
∴ ∆ OMP ≅ ∆ ONP (By R.H.S congruence rule)
We know that,
Corresponding parts of congruent triangles are equal.
∴ MP = NP = y(let) (By C.P.C.T.) .....(2)
From figure,
⇒ CP = CN - NP = x - y and PB = MB - MP = x - y
∴ CP = PB.
From figure,
DP = CD - CP = a - (x - y) and AP = AB - BP = a - (x - y)
∴ AP = PD.
Hence, proved that if two equal chords of a circle intersect within the circle, the segments of one chord are equal to corresponding segments of the other chord.
Circles — Interactive Study Guide
Circle Theorems Quick Reference
- Equal chords ⇔ equal central angles
- Perpendicular from centre bisects the chord
- Equal chords ⇔ equidistant from centre
- Central angle = 2 × inscribed angle (same arc)
- Angles in same segment are equal
- Angle in semicircle = 90°
- Opposite angles of cyclic quad = 180°
Problem-Solving Toolkit
Quick Self-Check
- Inscribed angle = 35°. Central angle for the same arc? (70°)
- Chord = 10 cm, distance from centre = 12 cm. Radius? (√(25+144) = √169 = 13 cm)
- ABCD is cyclic, ∠A = 95°. Find ∠C. (85°)