CCSS.Math.Content.HSG-CO.C

CCSS.Math.Content.HSG-CO.C is a cluster heading. These are the individual standards under it.

• CCSS.Math.Content.HSG-CO.C.10

  Prove theorems about triangles.

• CCSS.Math.Content.HSG-CO.C.11

  Prove theorems about parallelograms.

• CCSS.Math.Content.HSG-CO.C.9

  Prove theorems about lines and angles.

01

What Students Need to Do

Students use givens, definitions, postulates, and earlier results to build a logical argument. They explain why each step follows, using diagrams and precise geometric language.

02

What Mastery Looks Like

Students identify the given information, the claim, and a valid chain connecting them. They write a clear proof using definitions, postulates, and previously established results.

03

Common Misconceptions

Students often trust how a diagram looks instead of using the given facts. They may use circular reasoning, confuse a theorem with its converse, or skip reasons between steps.

04

How to Assess It

Give students a diagram of parallel lines cut by a transversal. Ask them to prove one pair of alternate interior angles is congruent and justify every step.

1. 01

   Use patty paper to test vertical angles, then label a diagram and turn observations into a two-column proof.

2. 02

   Give two proofs of the same triangle result and ask students to identify each claim, reason, and hidden assumption.

3. 03

   Run a proof card sort where teams arrange shuffled statements and reasons, then defend any step that could appear in two places.

4. 04

   Analyze a roof truss diagram and prove which angles or segments must match before checking the drawing's measurements.

• CCSS.Math.Content.HSG-SRT.B.4

  Prove theorems about triangles.

• CCSS.Math.Content.HSG-GPE.B.4

  Use coordinates to prove simple geometric theorems algebraically.

• CCSS.Math.Content.HSG-GPE.B

  Use coordinates to prove simple geometric theorems algebraically