The measure of each angle in an equilateral triangle is 60 degrees.
1. Triangle ABC is equilateral. 1. Given.
2. Triangle ABC is equiangular. 2. Equilateral triangles are equiangular.
3. / A = / B = / C 3. Definition of equiangular.
4. / A + / B + / C = 180. 4. Triangle sum theorem.
5. / A + / A + / A = 180. 5. Substitution.
6. 3 / A = 180. 6. Angle addition.
7. / A = 60. 7. Division property.
8. / B = 60. 8. Substitution.
9. / C = 60. 9. Substitution.