Inscribed Angle Math Example 2

Follow the full solution, then compare it with the other examples linked below.

Example 2

medium
In circle OO, inscribed angle ABC\angle ABC intercepts arc ACAC. If arc AC=134°AC = 134°, and arc CD=70°CD = 70°, find inscribed angle ADC\angle ADC that intercepts arc ACAC from the same side.

Solution

  1. 1
    Step 1: Note that ABC\angle ABC and ADC\angle ADC both intercept the same arc ACAC from the same side of the chord ACAC (both vertices on the major arc side).
  2. 2
    Step 2: By the Inscribed Angle Theorem, any inscribed angle intercepting the same arc has the same measure: ADC=12×arc AC\angle ADC = \frac{1}{2} \times \text{arc } AC.
  3. 3
    Step 3: Substitute: ADC=12×134°=67°\angle ADC = \frac{1}{2} \times 134° = 67°.
  4. 4
    Step 4: Conclude that both ABC\angle ABC and ADC\angle ADC equal 67°67°, illustrating that inscribed angles intercepting the same arc are congruent.

Answer

ADC=67°\angle ADC = 67°
Inscribed angles that intercept the same arc are congruent. Both angles equal half the intercepted arc of 134°, which is 67°. The extra arc CD information was a distractor to test careful reading.

About Inscribed Angle

An angle whose vertex lies on the circle and whose sides are chords of the circle. Its measure is exactly half the measure of the intercepted arc.

Learn more about Inscribed Angle →

More Inscribed Angle Examples