Substitute and evaluate expressions
Use this page to review substitution questions before testing a similar expression in the solver tool.
What this topic means and what to look for first.
Substitution means replacing a variable with a given value.
The main risk is losing track of brackets or negative values.
One reliable route through the topic.
- 1Write the expression clearly.
- 2Replace each variable with the given value.
- 3Keep brackets around substituted negative values.
- 4Evaluate the arithmetic carefully.
See the method in action.
Evaluate 3x + 2 when x = 4
- Substitute 4 for x.
- This gives 3(4) + 2 = 12 + 2 = 14.
Evaluate x^2 - y when x = 3 and y = 5
- Substitute the values into the expression.
- This gives 3^2 - 5 = 9 - 5.
- So the answer is 4.
Things that commonly send the method off track.
- Forgetting brackets when substituting a negative number.
- Squaring the wrong value or applying operations in the wrong order.
Want to test your own problem next?
Use the public page first, then create a free account if you want to try the solver beta on a typed question or photo.
A free account is the current follow-up route for returning to the solver beta and future guide updates as the public library grows.
Want to try a similar problem yourself?
Create a free account if you want to use the solver beta after reading the guide.
A free account is the current follow-up route for returning to the solver beta and future guide updates as the public library grows.
Extra algebra revision resources
If you want more printed algebra practice after this page, these broader searches are a sensible next step.
Amazon
Algebra workbook and revision book search
Useful if you want more equation, factorising, and worked-example practice in one printed source.
View Algebra workbook and revision book searchAmazon
GCSE algebra practice resources search
A wider GCSE-style search if you want more mixed algebra questions beyond one online guide.
View GCSE algebra practice resources searchFound this useful?
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Short answers worth checking.
Yes, especially if the substituted value is negative or raised to a power.
Check that every variable was replaced and that the final arithmetic was completed in the right order.
Continue with the next closely related topic.
Use the public site structure first, then switch into the solver tool only if you need a direct test.
CureMath uses artificial intelligence to suggest how a maths problem could potentially be solved. AI can make mistakes.
Check important answers independently before relying on them.