Then, why is the other purple angle equal to \(90^{\circ} - a?\)

Well, this is because if you start at the yellow angle that is \(\angle a\) and then look at the purple angle that right next to the box corner that is adjacent to it, you can see that these three angles together make up a line:

This is because a line has \(180^{\circ}\) degrees, and the right corner accounts for \(90^{\circ}\) of these degrees.

I hope this helps!

]]>Given what we know about trapezoids (namely that one pair of sides is perpendicular), it doesn't matter if the left and right sides aren't parallel. We just need to know that the top and bottom are parallel.

Happy Learning,

The Daily Challenge Team

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