Florida B.E.S.T. MA.8.GR.1.5
The Standard
Solve problems involving the relationships of interior and exterior angles of a triangle.
Florida B.E.S.T. Standards for Mathematics
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students find unknown interior and exterior angle measures in triangles. They use the 180° triangle sum, supplementary adjacent angles, and the sum of the two remote interior angles.
What Mastery Looks Like
- Students correctly find missing interior and exterior angle measures from a diagram or written problem. They write equations using the triangle sum, a linear pair, or the two remote interior angles.
Common Misconceptions
- Students may add an exterior angle to all three interior angles and set the sum equal to 180°. They may confuse the exterior angle with its adjacent interior angle or use only one remote interior angle.
How to Assess It
- Give this exit ticket: A triangle has interior angles of 47° and 68°, and one side is extended at the third vertex. Find the third interior angle and the exterior angle, showing both equations.
Lesson moves
Ways to Teach It
Cut corners from a paper triangle and align them on a line, then extend one side and compare the exterior angle with remote angles.
Ask students to write why an exterior angle equals the sum of the two remote interior angles, using a labeled diagram.
Give pairs a card sort matching triangle diagrams, missing-angle equations, and solutions, then have them correct one mismatched set.
Show a triangular roof truss with one beam extended, give two interior angles, and have students calculate the outside angle.
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Related Standards
- MA.8.GR.2.4
Solve mathematical and real-world problems involving proportional relationships between similar triangles.
- MA.8.GR.1.4
Solve mathematical problems involving the relationships between supplementary, complementary, vertical or adjacent angles.
- MA.912.GR.1.3
Prove relationships and theorems about triangles. Solve mathematical and real-world problems involving postulates, relationships and theorems of triangles.
- MA.912.T.1.4
Solve mathematical problems involving finding the area of a triangle given two sides and the included angle.
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