Question

In isoceles trapezoid ABCD, side CD is parallel to to side AB, line segment AC is congruent to line segment BD.The degree measure of angle BDC = ${80}^o$. Find the measures of the $\angle A$.

• A. ${90}^o$
• B. ${100}^o$
• C. ${110}^o$
• D. ${120}^o$

Answer 1

The correct option is B ${100}^o$

As per the property of isosceles trapezoid,
Opposite sides of an isosceles trapezoid are the same length (congruent) and the angles on either side of the bases are the same size (congruent).
So, Angle C $=$ ${80}^o$
Since the top and bottom angles are supplementary,

We know that,
Angle A $=$ ${180}^o-{80}^o$
Angle A $=$ ${100}^o$
Similarly, the Angle of B $=$ ${100}^o$