To complete step 7 of your proof, we will subtract the sum of the interior angles from the total sum calculated in step 6. Here's how it looks:
Completed Proof:
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Consider a triangle with interior angles ∠2, ∠4, and ∠6 and corresponding exterior angles ∠1, ∠3, and ∠5.
Reason: given -
\( m∠1 + m∠2 = 180° \)
\( m∠5 + m∠6 = 180° \)
\( m∠3 + m∠4 = 180° \)
Reason: Definition of Linear Pairs -
\( (m∠1 + m∠2) + (m∠5 + m∠6) + (m∠3 + m∠4) = 180° + 180° + 180° \)
Reason: addition -
\( (m∠2 + m∠4 + m∠6) + (m∠1 + m∠3 + m∠5) = 540° \)
Reason: rearrange and simplify -
\( m∠2 + m∠4 + m∠6 = 180° \)
Reason: Triangle Angle Sum Theorem -
\( 180° + (m∠1 + m∠3 + m∠5) = 540° \)
Reason: substitution -
\( m∠1 + m∠3 + m∠5 = 360° \)
Reason: Subtraction Property of Equality
So, the final statement is that the sum of the measures of the exterior angles of a triangle \( m∠1 + m∠3 + m∠5 = 360° \).