Question

Part EIf you use opposite operations to subtract the measure of angle C from both sides, what are you left with? What do you think that means?

Answer 1

Consider the equation:

`\angle A+\angle B+\angle C=\angle C+\angle D`

Substracting angle C from both sides gives:

`\begin{gathered} \angle A+\angle B+\angle C-\angle C=\angle C-\angle C+\angle D \\ \angle A+\angle B=\angle D \end{gathered}`

Therefore the resulting equation is:

`\angle A+\angle B=\angle D`

This implies that the exterior angle is the sum of the two opposite angles.