Hi Steffie,

What else do you know about the parallelogram? You need to know more than just the lengths of the four sides. The four parallelograms in the diagram below all have the same side lengths and yet the interior angles are quite different. Their measures can range from 0 degrees to 180 degrees.

If you know the measure of one of the interior angles you can determine the measure of the other three. If you know the side lengths and the length of one of the diagonals then the law of cosines will allow you to find the measure of one of the interior angles and hence the measure of the remaining three.

I hope this helps,
Penny