CCSS.Math.Content.7.G.A.2
The standard
Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.
Common Core State Standards for Mathematics · Geometry
What this standard means
Students need to draw shapes from given conditions, not just recognize finished shapes. They should use a ruler, protractor, compass, or geometry software to build triangles from side lengths and angle measures, then decide if the information makes one triangle, several possible triangles, or no triangle.
Mastery means students can test conditions, explain why a triangle works or fails, and compare different classmates' drawings for the same set of measures. Common sticking points are inaccurate measuring, thinking any three side lengths make a triangle, and missing that some angle or side combinations can create different triangles.
Ways to teach it
- Give pairs straws cut to 4 cm, 6 cm, and 11 cm, then ask them to try building a triangle and record what happens.
- Ask students to write: Which set gives exactly one triangle, 5 cm, 7 cm, 9 cm or angles 40, 60, 80, and why?
- Show three measure sets on the board and have students label each as one triangle, many triangles, or no triangle on an exit ticket.
- Have students sketch a simple roof truss using given side lengths, then explain whether the measurements force one exact shape.
Plan a lesson for CCSS.Math.Content.7.G.A.2
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