Quadrilateral abcd is inscribed in this circle. what is the measure of ∠a ? enter your answer in the box. ° a quadrilateral inscribed in a circle. the vertices of quadrilateral lie on the edge of the circle and are labeled as a, b, c, d. the interior angle c is labeled as 121 degrees.

The measure of angle A is 59 degrees.

When you have a quadrilateral inscribed in a circle the opposite sides are always supplementary (add to 180). Given the order of the vertices of our quadrilateral, we know that A and C are opposite.

Therefore, we can write and solve the following equation.
A + C = 180
A + 121 = 180
A = 59 degrees

Equatorial triangle and obtuce angle