nna is trying to determine if this quadrilateral is an isosceles trapezoid. First, she uses the slope formula and finds that AB || DC. Which other step must Anna take before she makes a determination? A) Use the slope formula to determine if AD || BC. B) Use the distance formula to determine if AB = CD. C) Use the distance formula to determine if AD = BC. D) Use the slope formula to determine if AD ⊥ AB.

In a trapezoid, exactly two opposite sides are parallel.
The other two opposite sides are not parallel, so checking slopes of the other two sides will not help.
In an isosceles trapezoid, the non-parallel sides are congruent, so she must use the distance formula on the other two sides to determine if the non-parallel sides are congruent.
The non-parallel sides are sides AD and BC.

Answer: Choice C