Understanding how to find a missing angle in a triangle is a key geometry skill for upper‑elementary and middle‑school students. This set includes four free printable worksheets that give students practice with right triangles, isosceles triangles, equilateral triangles, and scalene triangles.
Answer keys are included for all worksheets.
How to Find a Missing Angle in a Triangle
All triangles have interior angles that add up to 180°. To find a missing angle:
- Add the two known angles.
- Subtract that total from 180°.
- The result is the missing angle.
This rule works for every type of triangle:
- Right triangles — one angle is always 90°.
- Isosceles triangles — two angles are equal.
- Equilateral triangles — all angles are 60°.
- Scalene triangles — all angles are different.
Example Problem
A triangle has angles of 40° and 65°. What is the missing angle?
40° + 65° = 105°
180° − 105° = 75°
The missing angle is 75°.
Free Printable Worksheets
Each worksheet includes a variety of triangle types and increasing difficulty levels.
Worksheet 1 Worksheet 2 Worksheet 3 Worksheet 4These worksheets are ideal for 4th‑grade geometry, 5th‑grade math, and middle‑school review. They work well for homeschool lessons, classroom warm‑ups, independent practice, and general test preparation. Each worksheet is designed to be simple, clear, and easy to print.
Why This Skill Matters
Finding missing angles helps students build:
- Understanding of geometric rules
- Problem‑solving skills
- Algebra readiness
- Confidence with multi‑step reasoning
It’s a foundational concept that appears in many later math topics.
Related Worksheets
Statistics Worksheets – Mean, Mode, Range, Minimum and Maximum Values
In these statistics worksheets, students are asked to complete the graph using the given data set and find the mean, mode, range, and minimum and maximum values. The frequency is how often a value occurs in the data set.The mean
Order of Operations Worksheets (PEMDAS): Single Parentheses
These Order of Operations worksheets are designed to give students practice evaluating math expressions using PEMDAS. Each printable worksheet includes a variety of problems that help reinforce the correct order of operations. They’re designed for use in classrooms or homeschool,
Statistics Worksheets: Minimum, Maximum, Mean, Median, Mode, Range
These free printable statistics worksheets help students practice calculating the minimum, maximum, mean, median, mode, and range for different sets of numbers. Each worksheet includes four data sets and space for students to show their work. These printables are ideal
Prime Factorization Worksheets with Factor Trees
Strengthen math skills with this collection of free prime factorization worksheets. Students break down numbers into their prime factors using factor trees, a simple visual method for organizing the steps of prime factoring. These printable worksheets are ideal for reinforcing
1 Step Equations Worksheets for Pre-Algebra
Solving one‑step equations is one of the first major skills students learn in Pre‑Algebra and Algebra 1. These worksheets help students practice solving one‑step equations using addition or subtraction. The practice sheets below include 15 problems per page, along with
Order of Operations Worksheets (PEMDAS): Nested Parentheses
These order of operations worksheets with nested parentheses give students practice working through more complex expressions using PEMDAS. Each printable worksheet includes problems that feature two or more layers of parentheses, helping learners apply the order of operations. These worksheets