A plane, convex quadrilateral is a trapezoid if, and only if, two of the sides are parallel sides.
Next we will present the Trapezoid Elements and the classification of sides and angles.
Next, we will explore the property of a random trapezoid and two properties of the isosceles trapezoid.
What do you notice about the angles [math]\alpha[/math] and [math]\gamma[/math] and what about the angles [math]\beta[/math] and [math]\delta[/math]? Check the box "Show / Hide lines that pass through A and C and B and D and angles ζ and ε" and prove the argument of this property. [br]
What can you notice about the base angles when the trapezoid is an isosceles one? Check the box "Show / Hide Perpendicular Lines to Bases by D and C, Right Angles" and justify the property.