Question

name two pairs of congruent angles in each figure. justify your answer. 20. diagram with lines ab and cd intersecting at o 21. diagram with lines ef, ig, and ih forming right - angled intersections

Explanation:

Step1: Identify vertical - angle property for 20

Vertical angles are congruent. In figure 20, $\angle AOD$ and $\angle BOC$ are vertical angles, and $\angle AOC$ and $\angle BOD$ are vertical angles.

Step2: Identify right - angle property for 21

All right angles are congruent. In figure 21, $\angle EIF$ and $\angle GIH$ are right angles, and also $\angle EIG$ and $\angle FIH$ are congruent as they are both composed of two right - angles.

Answer:

For 20: $\angle AOD$ and $\angle BOC$, $\angle AOC$ and $\angle BOD$;
For 21: $\angle EIF$ and $\angle GIH$, $\angle EIG$ and $\angle FIH$