An interior angle of a regular polygon is 135°. The polygon is a/an:

The correct answer is Option (4) → octagon

At each vertex the interior and exterior angles add up to 180°, and the exterior angles of any polygon add up to 360°. In a regular polygon they are all equal, so the number of sides is 360° divided by one exterior angle.

• Exterior angle \(=180^\circ-135^\circ=45^\circ\)

• Number of sides \(=360^\circ\div45^\circ=8\), so the polygon is an octagon