Question

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Answer 1

Since the trapezoid is isosceles, the legs are congruent and the base angles are congruent.
That makes the two distances marked d equal.

Answer 2

What is distance d?

Answer 3

C?

Answer 4

Look at the coordinates of the upper left vertex, (a, b).
You see where coordinate a is on the x-axis?

Answer 5

The distance of a coordinate point and the origin is simply the absolute value of the coordinate. On the x-axis, a is simply a units from the origin, so distance d is simply a.