we know that
The quadrilateral ABCD is a isosceles trapezoid. The properties of the isosceles trapezoid are as follows:
-The lower base angles are congruent.
So
m∠A=m∠D
m∠B=m∠C
m∠A+m∠B=°
m∠D+m∠C=°
therefore
m∠D=m∠A=°
m∠B=-m∠A
m∠B=-
m∠B=°
m∠C=m∠B=°
<u>the answer is</u>
The measure of angle ADC is °