Evaluate by Substitution
When you evaluate an expression by substitution, you replace each variable with the given value, then simplify using the order of operations.
1) Substitute carefully
- Write the expression first.
- Replace every variable with its assigned value.
- Use parentheses around substituted values, especially if a value is negative or if the variable is multiplied by a number.
2) Simplify in order
- Do parentheses first.
- Then exponents, multiplication/division, and finally addition/subtraction.
- Keep the signs correct as you simplify.
3) Check your result
- Make sure every variable was replaced.
- Recompute if the answer seems unreasonable.
- If you used a negative value, verify that signs were handled correctly.
Example method
If an expression includes variables and numbers, substitute the given values, then simplify step by step until one number remains.
Common mistakes
- Forgetting parentheses around negative numbers
- Mixing up subtraction and a negative sign
- Skipping the order of operations
A correct final answer should be a single simplified value.