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Triangle Angle Sum Theorem

In the triangle below, move the vertices to change the interior angle measures

1. As you change the (3) interior angle measures, what remains constant?

The Triangle Angle Sum Theorem: In a triangle, the sum of the measures of the three interior angles will equal 180 degrees. Angle 1 + Angle 2 + 3 = 180o

2. What is the measure of Angle C?

2. What is the measure of Angle C?

What is the measure of Angle C?

3. What type of triangle is triangle ABC?

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  • A
  • B
  • C
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4. What type of triangle is triangle RST?

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  • A
  • B
  • C
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5. Find the measure of <1.

5. Measure of Angle 1 =

6. Find the measure of Angle A.

Find the measure of Angle A.

7. Find the measure of Angle Y.

Angle Y =

8. If one angle of an isosceles triangle measures 120 degrees, one of the other angles will measure ___.

9. If one angle of an isosceles triangle measures 90 degrees, one of the other angles will measure ___.

10. One of the angles of a triangle measures 140 degrees. This triangle

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  • A
  • B
  • C
  • D
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Prove the triangle angle sum theorem by using parallel lines