Curriculum placement
Grade 7. This describes the skill, not a learner estimate.
When given measures make a triangle
Determine whether side and angle conditions define a triangle
Problem types
- Test a third side with the triangle inequality
- Which lengths make a triangle
- Possible third sides
- Conditions that determine a triangle
- How many triangles fit these measures
- Construct a triangle on a grid
Builds on
- Measuring angles
- Defining attributes of shapes · Useful idea
Whether three side lengths make a triangle depends on a defining attribute of triangles: the two shorter sides together must exceed the longest.
Leads to
- Congruence criteria for triangles · See it applied
Three given sides or angles that fix a triangle's shape are the conditions behind the congruence criteria.
- The laws of sines and cosines · See it applied
Three sides can form a triangle only if the triangle inequality holds, which a solver of oblique triangles checks first.
Related skills
- Angle sums and exterior angles · Related idea
Three angles can form a triangle only if they total 180 degrees, the angle sum theorem.
- Velocity and force as vectors · Related idea
Two vectors and their sum form a triangle, so the length of the sum must obey the triangle inequality.
- Supplementary, vertical, and adjacent angles · Shared foundations
Open the interactive map to explore lessons and skill connections.