Question

Quadrilateral BIRD is inscribed in circle O.
What is the measure of angle D?

Answer 1

63

Explanation:

Answer 2

Answer:

∠D = 63°

Explanation:

Because all four corners of the quadrilateral rest on the circumference of the circle, then BIRD is a cyclic quadrilateral (circle theorem).

According to circle theorem, opposite angles of a cyclic quadrilateral are supplementary (sum to 180°).

∴ ∠I + ∠D = 180°

⇒ ∠D = 180° - ∠I

⇒ ∠D = 180° - 117° (since ∡I = 117°)

∴ ∠D = 63°