The lesson

This lesson teaches Angle Relationships. Read each section in order, work through every example on paper, then use the practice problems and quick check at the bottom.

The key relationships

When you study the key relationships, slow down and write one example in your notebook without looking at the screen. That active step is what turns reading into learning.

1Complementary angles add to 90°.
2Supplementary angles add to 180°.
3Vertical angles (across an X) are equal.
4Adjacent angles share a side and a vertex.

Two angles are supplementary. One is 110°. Find the other.

1Supplementary angles add to 180°.
2180° - 110° = 70°.

Why this matters

Angle Relationships shows up constantly in use complementary, supplementary, vertical, and adjacent angles to find unknowns. It also connects to what you will see on homework, quizzes, and the next unit in this grade.

Teachers often move fast in class. This page is here so you can pause, re-read, and practice until the idea feels familiar, not just until you have memorized a rule for one day.

Common mistakes to avoid

Rushing to the answer without writing steps. Middle-school math rewards clear work, and you catch errors earlier when steps are visible.

Mixing up similar ideas from the same topic. If two terms feel alike, make a two-column note: what is the same, what is different, and one example of each.

Key ideas from this lesson

The key relationships
Complementary angles add to 90°.
Supplementary angles add to 180°.
Vertical angles (across an X) are equal.
Adjacent angles share a side and a vertex.

Video walkthrough

Math Antics

Angle Basics

Right, acute, obtuse, complementary, and supplementary angles.

Watch on YouTube

Practice

For each problem: write your work in the box, type your answer, and check it. If you are stuck, reveal the solution one step at a time. Do not skip straight to the final answer.

Exercise 1

Try it yourself

Two angles are complementary. One measures 28°. Find the other.