∠1 and ∠2 form a linear pair, so ∠1 and ∠2 are supplementary by the <u>LINEAR PAIR POSTULATE</u> . Therefore, m∠1 +<u>m∠2</u> = 180° by the definition of supplementary. It is given that ∠2 ≅ <u>∠3</u> so m∠2 = m∠3 by the <u>ANGLE CONGRUENCE POSTULATE</u> . By substitution, m∠1 + m∠3 = 180°, so ∠1 and ∠3 are supplementary by the definition of supplementary.
Sample Response: Both are correct. As long as inverse operations and the properties of equality are used properly, both methods will generate the same solution. They both isolate the variable on one side of the equation.