91Ó°ÊÓ

Congruent angles are the angles that have equal measures.

Acute angles are the angles which measures between $\mathbf{0}\mathbf{°}$and $\mathbf{90}\mathbf{°}$.

From the figure, it can be observe that $∠AOB$and $∠HOG$are both congruent and acute angles, that is, both measures $20°$and is less than $90°$.

Therefore, a pair of congruent acute angles is $\left(∠AOB,∠HOG\right)$.

Congruent angles are the angles that have equal measures.

Right angle is an angle which measures exactly $\mathbf{90}\mathbf{°}$.

From the figure, it can be observe that $∠AOC$and $∠COH$are both congruent and right angles, that is, both measures exactly $90°$.

Therefore, a pair of congruent right angles is $\left(∠AOC,∠COH\right)$.

Congruent angles are the angles that have equal measures.

Obtuse angles are the angles which measures between $\mathbf{90}\mathbf{°}$and $\mathbf{180}\mathbf{°}$.

From the figure, it can be observe that $∠AOG$and $∠HOB$are both congruent angles and obtuse angles that is, both measures $160°$and are less than $180°$.

Therefore, a pair of congruent obtuse angles is $\left(∠AOG,∠HOB\right)$.