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# Central Angles and Intercepted Arcs - Problem 1

###### Brian McCall

###### Brian McCall

**Univ. of Wisconsin**

J.D. Univ. of Wisconsin Law school

Brian was a geometry teacher through the Teach for America program and started the geometry program at his school

A **central angle** is an angle with its vertex at the center of a circle, whose legs intersect the circle. The measure of a **central angle** is the same as the measure of the **arc** of its endpoints. Therefore, if central angle ∠ABC has measure 155°, then arc AC also has a measure of 155°.

Recall that a **chord** is a line that connects the intersections of a central angle with the circle. If two chords are congruent, their central angles are also congruent.

We can apply what we know about central angles and congruent chords in a circle to a problem like this. Well, we’re trying to find two different things, one the measure of angle B and two the measure of arc A.

Let’s start with the measure of arc A. if I look at A, it is the intercepted arc of this central angle, 155 degrees. So if I go back to what I know about a central and its intercepted arc, we said that they’re going to be equal to each other, which means A has to be equal to 155 degrees. Also this is the measure of arc A, is 155 degrees.

Second variable we’re solving for is B. If I look at B, it is the central angle that intersects a chord that is congruent to this central angle of 82 degrees, which means these two must be congruent something that we noticed when we said congruent chords have congruent central angles and congruent arcs, which means if B is congruent to 82, then B must be 82 degrees.

So the key here was remembering that chords have congruent, if the chords are congruent they have congruent central angle and that the central angle is congruent to its intercepted arc.

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###### Brian McCall

B.S. in Chemical Engineering, University of Wisconsin

J.D. University of Wisconsin Law School (magna cum laude)

He doesn't beat around the bush. His straightforward teaching style is effective and his subtle midwestern accent is engaging. There's never a dull moment with him.

so my teacher can't explain this in 5 weeks but I learn this in less than 3 minutes”

its hard to focus when the teacher is really really really goodlooking”

i like how it took you 3 minutes and 8 seconds to accomplish what my teacher couldn't in 3 days”

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## Johareliz · 5 months, 2 weeks ago

This helps me alot Thankyou:)