Using an indirect proof:

Assume that the figure is a trapezoid.

All trapezoids are quadrilaterals.

All quadrilaterals’ interior angles add up to 360° because any n-gon’s interior angles add up to 180(n-2)°.

We are given that the trapezoid has three right angles.

All right angles are 90°, thus these right angles have a total measure of 270°.

We can conclude fourth angle must be 90°.

If it has four right angles, it is a rectangle.

Rectangles have two sets of parallel sides.

However, trapezoids have exactly one set of parallel sides.

Alas, our figure cannot be a trapezoid.

Not possible trapezoid is a quadrilateral with 4 angles and 4 sides which means the interior measure =360 if 3 angles are right the 4th angle must be a right angle a trapezoid does not have 4 right angles, it only has one pair of parallel sides