A rhombus crosses at a right angle

Draw a rhombus with all sides 5. Draw both diagonals with a ruler. What angle do they cross at?

The diagonals cross at exactly 90°.

Rule: A rhombus has four equal sides. Four equal sides make its diagonals cross at exactly 90°. That holds whatever its corners measure.

Why? The diagonals halve each other. So the four small triangles have the same three side lengths. Their angles at the crossing are equal. Four equal angles total 360°, so each is 90°.

A 10 by 5 rectangle's diagonals cross at about 53°, not 90°. Square corners are a different demand from equal sides.

A square is both a rectangle and a rhombus. Its diagonals are equal, like a rectangle's. They also cross at 90°, like a rhombus's.

Tap Next shape. Read the angle at the crossing.

Try the lab to finish this lesson.