Vertically Opposite Angles

Vertically Opposite Angles are the angles opposite each other when two lines cross

In this example, a° and b° are vertical angles.

The interesting thing here is that vertical angles are equal:

a° = b°

(in fact they are congruent angles)

Because b° is vertically opposite 40°, it must also be 40°

A full circle is 360°, so that leaves 360° - 2×40° = 280°

Angles a° and c° are also vertically opposite, so must also be equal, which means they are 140° each.

Answer: a = 140°, b = 40° and c = 140°.

Language Note: "Vertically Opposite Angles" are usually called Vertical Angles in the US