Students will learn what complementary and supplementary angles are. Then they'll learn how to find one missing angle, given that both angles are complementary or supplementary. Students will learn how to do this for both degrees and radians. Finally, students will practice solving linear equations involving complementary and supplementary angles in degrees. Here's an example. Before attempting this section, you should know how to solve two-step equations.

Some of these problems involve solving multi-step equations. Should combining like terms be considered a "step" in solving linear equations? (I now realize the answer is no. A step should be an operation which alters both sides. For example, divide both sides by two. I will have to bring some of the videos from solving multi-step equations into the two-step bucket.)

Watch these Khan Academy videos:

- Find measure of angles word problem
- Equation practice with supplementary angles
- Equation practice with complementary angles
- Triangle exterior angle example
- Worked example: Triangle angles (intersecting lines)
- Worked example: Triangle angles (diagram)
- Triangle angle challenge problem 2
- Vertical angles
- Vertical angles are congruent proof
- Complementary & supplementary angles

Do these Khan Academy exercises:

- Create equations to solve for missing angles
- Finding angle measures between intersecting lines
- Unknown angle problems (with algebra)
- Vertical angles
- Identifying supplementary, complementary, and vertical angles
- Complementary and supplementary angles (no visual)
- Complementary and supplementary angles (visual)
- Finding missing angles

Next, give your students these challenges:

- Sweeping Hands by NRICH
- Painting Possibilities by NRICH

Conclude by leading this investigation:

Graphene Trampoline (logic & probability)

by MathPickle

7.G.B.5: Use facts about supplementary, complementary, vertical, and adjacent angles in a multi-step problem to write and solve simple equations for an unknown angle in a figure.