Maryland Math 8.GR.A.2
The Standard
Draw or build triangles using tools (ruler, protractor, technology, or physical manipulatives) given three measures of angles or sides. Determine whether the given conditions result in a unique triangle, more than one triangle, or no triangle.
Maryland College and Career Ready Standards for Mathematics (2025) · MAKE CONJECTURES ABOUT AND VERIFY GEOMETRIC RELATIONSHIPS.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students draw or build triangles from three given measurements. They decide whether the measurements make one triangle, more than one, or none. Rotated and flipped copies count as the same triangle.
What Mastery Looks Like
- Students check whether side lengths can meet and whether angles add to 180°. They can draw two different triangles when the measurements allow more than one and explain why three valid angles do not fix a triangle's size.
Common Misconceptions
- Students may think any three side lengths can make a triangle, or that three angles fix its size. Some count a flipped triangle as a new one or assume two sides and one angle always make exactly one triangle.
How to Assess It
- Give an exit ticket with three sets: sides of 3, 4, and 5 cm; sides of 2, 3, and 6 cm; and angles of 50°, 60°, and 70°. Ask students to label each set one, more than one, or none, and explain one choice.
Lesson moves
Ways to Teach It
Join 3 cm, 4 cm, and 5 cm straws with pipe cleaners, then try 2 cm, 3 cm, and 6 cm straws.
Sketch two triangles with angles of 50°, 60°, and 70°, then explain why different side lengths still fit.
Give pairs cards showing 5-7-9 sides, 90°-60°-40° angles, and 100°-50°-30° angles; have them sort the cards into one, many, or none.
Show a roof truss sketch with beams of 5 m, 7 m, and 9 m, then ask whether those lengths fix its shape.
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