Answer:
use the symmetric and transitive properties of congruence
Explanation:
(1) ∠ABC ≅ ∠DEF and ∠GHI ≅ ∠DEF; given
(2) ∠DEF ≅ ∠GHI; symmetric property of congruence
(3) ∠ABC ≅ ∠GHI; transitive property of congruence (QED)
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Additional comment
The transitive property says if A≅B and B≅C, then A≅C. We used the symmetric property to swap sides of the congruence symbol with DEF and GHI to put the statement in the form to match the transitive property.
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You will note we used the form ...
(statement number) statement; reason
with statement and reason separated by a semicolon.