In the given figure above
O
is the centre of the circle,
BC
and
CD
are two equal chords and
. You have to find sum of
(in degrees).
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Join OC. As OB = OC = Radius of circle, so ∠ O B C = ∠ O C B = 7 0 ∘ . Applying angle sum property in △ BOC, we get ∠ B O C = 4 0 ∘ .
Now, ∠ B O C = ∠ C O D = 4 0 ∘ {As angle formed by equal chords on the center are equal}.
∠ B A C = 2 1 ∠ B O C = 2 1 4 0 ∘ = 2 0 ∘ {As angle made by a chord on the circumference is half the angle made by it on the center}.
∠ B A C = ∠ C E D = 2 0 ∘ {As angle formed by equal chords on the circumference are equal}.
∠ B F D = 2 1 ∠ B O D = 2 1 8 0 ∘ = 4 0 ∘ . {As angle made by a chord on the circumference is half the angle made by it on the center}
We have to find ∠ B A C + ∠ B F D + ∠ C E D which is equal to 2 0 ∘ + 4 0 ∘ + 2 0 ∘ = 8 0 ∘ and that's our answer.