🧠 Triangle Theorems: Show Your Thinking (G-CO.C.10)

Paginepagineapp.com

Name:

Date:

Prove and apply theorems about triangles (angle sum, exterior angle, isosceles). Solve each problem and show your work.

1. A triangle has angles 27° and 44°. Third angle = ___

Show your work

2. Exterior angle of a triangle; remote interior angles 38° and 47°. Exterior angle = ___

Show your work

3. Isosceles triangle with vertex angle 68°. Each base angle = ___

Show your work

4. A triangle has angles 59° and 60°. Third angle = ___

Show your work

5. Exterior angle of a triangle; remote interior angles 28° and 25°. Exterior angle = ___

Show your work

6. Isosceles triangle with vertex angle 80°. Each base angle = ___

Show your work

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

Answer key: 1) 109° · 2) 85° · 3) 56° · 4) 61° · 5) 53° · 6) 50°

Love free resources? The free Pagine app tracks the books your child reads — kids earn streaks & badges. 📚 App Store · Google Play

← All worksheets

Free to print & share · pagineapp@mwamb.compagineapp.com

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 — problems with space to show work and explain reasoning, 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.

Frequently asked questions

Is this worksheet free?

Yes — it is free to print for home or the classroom. Sign in with a free Pagine account, then use the Print button or save it as a PDF.

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).

Where can I find grade 10 books to read with it?

Pagine's free library has 20,000+ children's books you can read in the Pagine e-reader or the free Pagine app — sorted by age and grade, with free audiobooks too.

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: Quick Check (G-CO.C.10)

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

📚 Read along: 20,000+ free books in the Pagine e-reader

Pair this grade 10 worksheet with a story. Pagine's free library has 20,000+ children's books — classic novels, drama, poetry and non-fiction, classics and free audiobooks — that you can read right in the Pagine e-reader on any phone, tablet or computer, with adjustable text size and night mode. No ads.

Browse free grade 10 books → · Grade 10 reading level · Free audiobooks · High school reading list

📱 Get the free Pagine app — log every book your child reads (scan the barcode or search), set reading goals, and watch streaks and badges grow. Download on the App Store · Get it on Google Play