## Trigonometry 7th Edition

In given figure 22, producing the line DC along vertical post to meet the horizontal at "B"- a right triangle ABC, right angled at B is formed as vertical posts are perpendicular to the horizontal- In right triangle ABC- $\angle A$ = α (Given) $\angle C$ = β ( Vertically opposite angles are same at intersection of two lines ) Therefore- α + β = $90^{\circ}$ (Sum of acute angles of a right triangle is always $90^{\circ}$ Hence α and β are complementary angles.