Write a paragraph proof to show that the base angles of an isosceles trapezoid are congruent?

Answer 1

To prove that the base angles of an isosceles trapezoid are congruent, consider an isosceles trapezoid ( ABCD ) with ( AB \parallel CD ) and ( AD \cong BC ). By the properties of parallel lines, the angles ( \angle DAB ) and ( \angle ABC ) are consecutive interior angles formed by the transversal ( AD ) and ( BC ), respectively, thus ( \angle DAB + \angle ABC = 180^\circ ). Similarly, the angles ( \angle ADC ) and ( \angle BCD ) also sum to ( 180^\circ ). Since ( AD \cong BC ) and the trapezoid is isosceles, the two pairs of opposite angles must be equal, leading to ( \angle DAB \cong \angle ABC ) and ( \angle ADC \cong \angle BCD ), proving that the base angles ( \angle DAB ) and ( \angle ABC ) are congruent.