Evaluating Expressions
Substitute values for variables and simplify.
Key idea
Substitute values for variables and simplify.
In depth
To evaluate, substitute a number for each variable (use brackets to protect it), then follow the order of operations. This turns the general formula into a specific value.
Worked example
Evaluate 2x² − 3x when x = −2: 2(−2)² − 3(−2) = 2(4) + 6 = 14.
Formula
Real-world uses
- Calculating the cost of a taxi ride from its formula
- Plugging temperatures into a conversion rule
Common mistake
Writing −2² instead of (−2)². Without brackets only the 2 is squared.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Evaluating Expressions?
Substitute values for variables and simplify. It is a topic at the beginner level in Algebra.
What is the formula for Evaluating Expressions?
The key formula is x=4 ⇒ 3x+2 = 14.
Where is Evaluating Expressions used in real life?
Real-world examples: Calculating the cost of a taxi ride from its formula; Plugging temperatures into a conversion rule.
What should I learn before Evaluating Expressions?
Make sure you are comfortable with Variables and Expressions, the previous topic in Algebra.
What is a common mistake with Evaluating Expressions?
Writing −2² instead of (−2)². Without brackets only the 2 is squared.
How can I practise Evaluating Expressions?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Evaluating Expressions?
Move on to Like Terms next.
Related beginner topics in Algebra
- Variables and Expressions – Letters stand for unknown or changing numbers in expressions.
- Like Terms – Terms with the same variable part can be combined.
- Distributive Property – Multiplication spreads over addition.
- Simplifying Expressions – Combine like terms and apply distribution to write expressions compactly.
- Writing Expressions from Words – Translate phrases like “three more than twice a number” into algebra.
- One-Step Equations – Undo one operation to isolate the variable.