🧠 Parallel Lines & Transversals: Show Your Thinking (G-CO.C.9)

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Prove and apply theorems about lines and angles. Solve each problem and show your work.

1. Parallel lines cut by a transversal. Corresponding angle to 115° = ___

Show your work

2. Same-side interior angle to 72° = ___

Show your work

3. Alternate interior angles: (3x + 6)° and 66°. x = ___

Show your work

4. Parallel lines cut by a transversal. Corresponding angle to 120° = ___

Show your work

5. Same-side interior angle to 101° = ___

Show your work

6. Alternate interior angles: (3x + 3)° and 63°. x = ___

Show your work

Explain: How did you solve problem 1? Could you check it another way?

Answer key: 1) 115° · 2) 108° · 3) 20 · 4) 120° · 5) 79° · 6) 20

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Worksheets › Grade 10 Math (Geometry) › Parallel Lines & Transversals › Parallel Lines & Transversals

Grade 10 (ages 15–16)Numbers & mathsFree printable PDF

About this grade 10 worksheet

Free Grade 10 Geometry math worksheet (Common Core G-CO.C.9): parallel lines & transversals — problems with space to show work and explain reasoning, with answer key. Skill: Prove and apply theorems about lines and angles. Level: Grade 10 — also suits Year 11 (UK).

For teachers: skills & standards

CCSS G-CO.C.9: Prove and apply theorems about lines and angles
Works as a morning-work page, a centre/station activity, homework or an early-finisher task.

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What age is it for?

It is designed for Grade 10 (ages 15–16), but use it with any child who is ready.

What skills does it build?

Prove and apply theorems about lines and angles.

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More “Parallel Lines & Transversals” printables (g-co.c.9: prove and apply theorems about lines and angles)

Parallel Lines & Transversals: Practice A (G-CO.C.9) · Parallel Lines & Transversals: Practice B (G-CO.C.9) · Parallel Lines & Transversals: Mixed Practice & Reasoning (G-CO.C.9) · Parallel Lines & Transversals: Quick Check (G-CO.C.9)

All 5 parallel lines & transversals sheets → · Grade 10 Math (Geometry): all 10 skills → · All Common Core grades

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