Answer:
Substitution Property
Step-by-step explanation:
So we know that:
[tex]m\angle A=m\angle B[/tex]
And we also know that:
[tex]m\angle A+m\angle C=\angle D[/tex]
And by using a specific property, we get that:
[tex]m\angle B+m\angle C=\angle D[/tex]
Essentially, we substituted B for A.
So, this is an example of the substitution property, where if two sides/angles are congruent, we can substitute them for each other.
