Combine like terms
You can add x’s to x’s and numbers to numbers — but not x’s to numbers. They are different things.
Worked example
Simplify 3x + 4 + x.
- 1
Spot the like terms. x on its own means 1x.
3x and 1x are alike; 4 is different
- 2
Add the x’s.
3x + 1x = 4x
- 3
Leave the 4 as it is.
4x + 4
Answer: 4x + 4
Check: Try x = 2: 3(2) + 4 + 2 = 12 and 4(2) + 4 = 12 ✓
⚠️ The usual mistake
Writes 3x + 4 = 7x.
Adding everything in sight looks like simplifying.
Fix: 3 apples + 4 oranges is not 7 apples. Test with a number: if x = 1, 3x + 4 is 7, but if x = 2 it is 10 — and 7x is 14.
💬 Say this
“Which things are the same kind? Apples with apples, oranges with oranges.”
🏠 Try it at home
Empty a pocket of mixed coins. “3 dimes + 4 pennies + 1 dime” — tidy it up. You can’t call it 8 dimes.
