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Bunuel
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We can see 5 arcs makes Total 180 degree angle at center.

Now, required angle = 2/5 *180 = 72 degree. (one arc makes angle = a/2, As angle made by joining two consecutive arcs = a)

So, I think C. :)
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Hello everyone

Here is my solution
The answer is 72
C

It is easier than the rest of the two problems
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By using the inscribed angle theorem, if an inscribed angle is x, the arc it subtends is equal to 2x.

See the image attached.

As per the problem statement congruent angles is x and let make y as the angle the line makes when it touches the circumference.
Let's measure the arc BF.
Angle BAF is x. We can represent arc BF as sum of arc BD and arc DF.
arc BF = arc BD + arc DF --(1)
Based on the theorem, angle BAF, subtends arc BF.
=> arc BF = 2x. --(2)


using (1) and (2)

arc BF = arc BD + arc DC
arc BF = 2(angle DEF) + 2(angle BCD)
arc BF = 2y + 2y
arc BF = 4y

We thus have:

arc(BF) = 4y = 2x
⇒ y = x/2

Sum of three angles of a triangle = 180°

2x+y = 180°
2x + x/2 = 180°
(5/2)x = 180°
x = 72°

So the answer choice is C
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