Symmetric property of congruence.
Solution:
Given statement:
If ∠1 ≅ ∠2, then ∠2 ≅ ∠1.
<em>To identify the property used in the above statement:</em>
Let us first know some property of congruence:
Reflexive property:
The geometric figure is congruent to itself.
That is
.
Symmetric property of congruence:
If the geometric figure A is congruent to figure B, then figure B is also congruent to figure A.
That is
.
Transitive property of congruence:
If figure A is congruent to figure B and figure B is congruent to figure C, then figure A is congruent to figure C.
That is 
From the above properties, it is clear that,
If ∠1 ≅ ∠2 then ∠2 ≅ ∠1 is symmetric property of congruence.