91Ó°ÊÓ

Angles having the measurement of when they added are referred as the complementary angles.

By using the definition make an equation that represents the addition of provided angles.

$∠4+∠6=90°$

According to the definition of vertically opposite angles are referred as those angles which are formed when a line travels from two separate lines and the measurement of these angles is the same.

The angles that are vertically opposite in the figure are $∠6$and $∠3$so make an equation by using the property of these angles.

$∠6=∠3$

Rewrite the equation$∠4+∠6=90°$ by substituting $∠3$at the place of $∠6$.

$∠3+∠6=90°$

The angles$∠3$ and$∠4$ are the part of$∠BCG$ so the measurement of$∠BCG$ will be 90°. Use the definition of perpendicular lines that is the relation between two lines is perpendicular when the measurement of angles formed by those lines is equal to 90°.

The angle$∠BCG$ is formed by the lines$\stackrel{→}{CG}$ and$\stackrel{↔}{AD}$ which means that the relation between these lines is perpendicular so make an equation for this and this will be the conclusion.

$\stackrel{→}{CG}âŠ\yen \stackrel{↔}{AD}$