The sum of the measures of the angles of a triangle is 180 degrees.
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____________________ \ /____________________
1 /2\3
________________________ /45\______________________
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1. / 1 + / 2 + / 3 = 180 1. Postulate 11: The sum of the
measures
of the angles with the
same
vertex on one side of a line is 180.
2. / 1 = / 4 2. Alternate interior angles are equal.
3. / 3 = / 5 3. Alternate interior angles are equal.
4. / 4 + / 2 + / 5 = 180 4. Substitution