In the diagram below, trapezoid ABCD, with bases AB and DC, is inscribed in circle O, with diameter DC. If mAB = 80, find mBC. 80° D

Elementary Geometry For College Students, 7e
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ISBN:9781337614085
Author:Alexander, Daniel C.; Koeberlein, Geralyn M.
Publisher:Alexander, Daniel C.; Koeberlein, Geralyn M.
ChapterP: Preliminary Concepts
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### Geometry Problem Explanation

#### Problem Statement:
In the diagram below, trapezoid \(ABCD\), with bases \(\overline{AB}\) and \(\overline{DC}\), is inscribed in circle \(O\), with diameter \(\overline{DC}\). If \(m\overset{\frown}{AB} = 80^\circ\), find \(m\overset{\frown}{BC}\).

![Trapezoid and Circle Diagram](https://turing.mu/assets/images/geometry.png) 

#### Diagram Description:
- A circle \(O\) with points \(A\), \(B\), \(C\), and \(D\).
- \( \overline{AB} \) and \( \overline{DC} \) are the two bases of the trapezoid \(ABCD\).
- \( \overline{DC} \) is the diameter of circle \(O\).
- An arc \(AB\) (from point \(A\) to point \(B\)) is 80 degrees.
- The trapezoid is inscribed in circle \(O\).

#### Solution Approach:
1. Understand that since \(\overline{DC}\) is the diameter, points \(D\) and \(C\) lie on the circle's circumference, making the circle a semicircle across \(\overline{DC}\).
2. The inscribed angle \(\overset{\frown}{ABC}\) subtended by arc \(\overset{\frown}{AB}\) (80 degrees) and arc \(BC\) must consider the circle's property, where the total angle around a point in a circle is \(360^\circ\).

#### Steps to Solve:
1. Calculate the full circle angle coverage: \(360^\circ\).
2. The arcs \(\overset{\frown}{AB}\) and \(\overset{\frown}{BC}\) should sum up to half the circle since \(\overline{DC}\) is the diameter: \(180^\circ\).
3. Given \(m\overset{\frown}{AB} = 80^\circ\), the remaining angle must be:
   \[
   180^\circ - 80^\circ = 100^\circ 
   \]
   Thus, \(m\overset{\frown}{BC} = 100^\circ\).

#### Summary:
Transcribed Image Text:### Geometry Problem Explanation #### Problem Statement: In the diagram below, trapezoid \(ABCD\), with bases \(\overline{AB}\) and \(\overline{DC}\), is inscribed in circle \(O\), with diameter \(\overline{DC}\). If \(m\overset{\frown}{AB} = 80^\circ\), find \(m\overset{\frown}{BC}\). ![Trapezoid and Circle Diagram](https://turing.mu/assets/images/geometry.png) #### Diagram Description: - A circle \(O\) with points \(A\), \(B\), \(C\), and \(D\). - \( \overline{AB} \) and \( \overline{DC} \) are the two bases of the trapezoid \(ABCD\). - \( \overline{DC} \) is the diameter of circle \(O\). - An arc \(AB\) (from point \(A\) to point \(B\)) is 80 degrees. - The trapezoid is inscribed in circle \(O\). #### Solution Approach: 1. Understand that since \(\overline{DC}\) is the diameter, points \(D\) and \(C\) lie on the circle's circumference, making the circle a semicircle across \(\overline{DC}\). 2. The inscribed angle \(\overset{\frown}{ABC}\) subtended by arc \(\overset{\frown}{AB}\) (80 degrees) and arc \(BC\) must consider the circle's property, where the total angle around a point in a circle is \(360^\circ\). #### Steps to Solve: 1. Calculate the full circle angle coverage: \(360^\circ\). 2. The arcs \(\overset{\frown}{AB}\) and \(\overset{\frown}{BC}\) should sum up to half the circle since \(\overline{DC}\) is the diameter: \(180^\circ\). 3. Given \(m\overset{\frown}{AB} = 80^\circ\), the remaining angle must be: \[ 180^\circ - 80^\circ = 100^\circ \] Thus, \(m\overset{\frown}{BC} = 100^\circ\). #### Summary:
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