Inscribed Angle Math Example 4

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

Example 4

hard
Quadrilateral ABCDABCD is inscribed in a circle. If A=82°\angle A = 82°, find C\angle C. Then, if arc AB=96°AB = 96° and arc BC=110°BC = 110°, find ADC\angle ADC.

Solution

  1. 1
    Step 1: Use the property that opposite angles of a cyclic quadrilateral are supplementary: A+C=180°\angle A + \angle C = 180°.
  2. 2
    Step 2: Solve for C\angle C: C=180°82°=98°\angle C = 180° - 82° = 98°.
  3. 3
    Step 3: To find ADC\angle ADC, note it intercepts arc ABCABC (the arc from AA to CC not containing DD). Arc ABC=arc AB+arc BC=96°+110°=206°ABC = \text{arc } AB + \text{arc } BC = 96° + 110° = 206°.
  4. 4
    Step 4: Apply the Inscribed Angle Theorem: ADC=12×206°=103°\angle ADC = \frac{1}{2} \times 206° = 103°.

Answer

C=98°\angle C = 98°; ADC=103°\angle ADC = 103°
Opposite angles in a cyclic quadrilateral sum to 180° because they intercept supplementary arcs that together form the full circle (360°). The inscribed angle ADC intercepts the combined arc AB+BC = 206°, giving half of that as 103°.

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