In the given figure, O is the centre of a circle, ∠ADC = 130° and chord BC = chord BE. Find ∠CBE.
Given: ∠ADC = 130° , BC = BE
We know that,
(exterior ∠AFC ) = (2×∠ADC)
(exterior ∠AFC ) = (2×130)
(exterior ∠AFC ) = 260
∠AFC = 360° – (exterior ∠AFC) = 360°–260° = 100°
∠AFB = ∠AFC + ∠CFB = 180°
∠AFC + ∠CFB = 180°
100° + ∠CFB = 180°
∠CFB = 180° – 100° = 80°
In quadrilateral ABCD
∠ADC + ∠ABC = 180° (opposite angles in cyclic quadrilateral are supplementary)
130° + ∠ABC = 180°
∠ABC = 180° – 130° = 50°
In ΔBCF
By angle sum property
∠CBF + ∠CFB + ∠BCF = 180°
50° + 80° + ∠BCF = 180°
∠BCF = 180° – 50° – 80° = 50°
Now,
∠CFE = ∠CFB + ∠BFE = 180°
∠CFB + ∠BFE = 180°
80° + ∠BFE = 180°
∠BFE = 180° – 80° = 100°
Here,
In ΔBCE
BC = BE (given)
∠BCE = ∠BEC = 50° (angles opposite to equal sides are equal)
By angle sum property
∠BCE + ∠BEC + ∠CBE = 180°
50° + 50° + ∠CBE = 180°
∠CBE = 180° – 50° – 50° = 100°
∴