Height of a parallelogram with fixed side lengths

This demonstration models a parallelogram made with sticks hinged at the vertices.

Move point C to change the shape of the parallelogram.
See how the height changes, while the side lengths don't change.
The side lengths of this parallelogram can be adjusted by sliders a and b.

When does the height of the parallelogram equal the length of the other sides (the two sides that are not bases)?

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Susan Addington, Created with GeoGebra