Skip to content

Physics Playground

Simulations How we teach Pricing

Language

Log in Start learning free

Loading…

Physics Playground

Built on open, peer-reviewed sources: OpenStax, The Feynman Lectures on Physics, HyperPhysics, NASA and NIST. See our sources.

Learn

Physics course
Math for Physics
Start with the math toolkit
Simulations
Glossary
Exercises
Past exams
Library
How we teach

Company

Pricing
Terms
Privacy
Contact

© 2026 Physics Playground. Made for the curious.Language

Exercises Equations and inequalities

Example 8.15 from Prealgebra, 8.2 Solve Equations Using the Division and Multiplication Properties of Equality

Solve Equations Using the Division and Multiplication Properties of Equality: example 8.15

Solve: $- r = 2 .$

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Solution
Remember $- r$ is equivalent to $−1 r .$

Rewrite $- r$ as $−1 r$ .

Divide both sides by $−1$ .

Check.

Substitute $r = −2$

Simplify.

In Solve Equations with Fractions, we saw that there are two other ways to solve $- r = 2 .$
We could multiply both sides by $−1 .$

We could take the opposite of both sides.

Your turn

The book's Try It right after this example: same idea, new numbers. Only the answer is given.

Solve: $- k = 8 .$

How did it go?

PreviousSolve Equations Using the Division and Multiplication Properties of Equality: example 8.14 Next Solve Equations Using the Division and Multiplication Properties of Equality: example 8.16

From Prealgebra (1st edition) by OpenStax (Rice University), section 8.2, licensed under CC BY 4.0. Original at openstax.org. We split the solution into steps; the words, numbers and figures are the book's. OpenStax doesn't endorse this site.