Let A, B be the centres of two circles of equal radii; draw them so that each one of them passes through the centre of the other. Let them intersect at C and D.

Examine whether $\overline{AB} \text{ and } \overline{CD}$ are at right angles.

Steps:

1. Draw a line segment AB of any suitable length.

2. With A as centre and radius equal to AB, draw a circle.

3. With B as centre and the same radius (equal to AB), draw another circle which passes through A.

4. Let the two circles intersect at points C and D.

5. Join CD.

On measuring the angle between $\overline{AB} \text{ and } \overline{CD}$, we see that they intersect at right angles.

Hence, $\overline{AB} \text{ and } \overline{CD}$ are at right angles.