✅ Triangle Theorems: Quick Check (G-CO.C.10)

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Prove and apply theorems about triangles (angle sum, exterior angle, isosceles). Work on your own. Then check your answers.

1. A triangle has angles 77° and 45°. Third angle = ___

2. Exterior angle of a triangle; remote interior angles 58° and 70°. Exterior angle = ___

3. Isosceles triangle with vertex angle 34°. Each base angle = ___

4. A triangle has angles 65° and 70°. Third angle = ___

5. Exterior angle of a triangle; remote interior angles 33° and 55°. Exterior angle = ___

6. Isosceles triangle with vertex angle 114°. Each base angle = ___

7. A triangle has angles 49° and 29°. Third angle = ___

8. Exterior angle of a triangle; remote interior angles 78° and 39°. Exterior angle = ___

9. Isosceles triangle with vertex angle 120°. Each base angle = ___

10. A triangle has angles 43° and 36°. Third angle = ___

Score: ____ / 10 I can prove and apply theorems about triangles (angle sum, exterior angle, isosceles): ☐ yes ☐ almost ☐ not yet

Answer key: 1) 58° · 2) 128° · 3) 73° · 4) 45° · 5) 88° · 6) 33° · 7) 102° · 8) 117° · 9) 30° · 10) 101°

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Worksheets › Grade 10 Math (Geometry) › Triangle Theorems › Triangle Theorems

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.10): triangle theorems — a ten-question quick check (quiz), with answer key. Skill: Prove and apply theorems about triangles (angle sum, exterior angle, isosceles). Level: Grade 10 — also suits Year 11 (UK).

For teachers: skills & standards

CCSS G-CO.C.10: Prove and apply theorems about triangles (angle sum, exterior angle, isosceles)
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 triangles (angle sum, exterior angle, isosceles).

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More “Triangle Theorems” printables (g-co.c.10: prove and apply theorems about triangles (angle sum, exterior angle, isosceles))

Triangle Theorems: Practice A (G-CO.C.10) · Triangle Theorems: Practice B (G-CO.C.10) · Triangle Theorems: Mixed Practice & Reasoning (G-CO.C.10) · Triangle Theorems: Show Your Thinking (G-CO.C.10)

All 5 triangle theorems sheets → · Grade 10 Math (Geometry): all 10 skills → · All Common Core grades

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