Can one formula find the 10th term instantly?
By the end of this lesson
Write a starter nth-term for an add-the-same sequence: first + (n−1)×step, and check it on n=1 and n=2.
Remember
- If each jump adds the same d, it is an arithmetic pattern.
- nth term (starter): first + (n − 1) × step.
- 5, 8, 11, 14… first=5, step=3 → 5 + (n−1)×3 = 3n + 2.
- Always check n=1 (must give the first term) and n=2 (must give the second).
- The point of an nth term is to jump to the 10th or 100th term without listing.
Worked examples
Cover the answer. Try the steps on paper, then open them.
Example 1 — Build 3n + 2
5, 8, 11, 14…
- first = 5, step = 8−5 = 3
- nth = 5 + (n−1)×3
- 5 + 3n − 3 = 3n + 2
- n=1 → 5 ✓ n=2 → 8 ✓
Answer: 3n + 2
Check: 10th term: 3(10)+2 = 32, no listing needed.
Example 2 — Another
2, 6, 10, 14…
- first=2, step=4
- 2 + (n−1)×4 = 4n − 2
- n=1 → 2 ✓ n=2 → 6 ✓
Answer: 4n − 2
Check: n=3 → 10 ✓.
Example 3 — Use it
For 3n + 2 find the 1st, 2nd and 10th terms.
- n=1 → 5
- n=2 → 8
- n=10 → 32
Answer: 5, 8, 32
Check: Plug n in. That is substitution again.
Common mistakes
Slip Using n instead of (n−1) steps from the first term and forgetting to check n=1.
Fix If n=1 does not give the first term, the formula is wrong.
Always test n=1.
Slip Step taken as the first term.
Fix Step is the jump: 8−5=3, not 5.
Subtract two neighbours.
Slip Listing 10 terms when you already have 3n+2.
Fix Plug n=10.
That is why the formula exists.
Try on paper first
Write the answer, then tap Reveal. These are not the quiz — they are warm-ups.
1. Step in 4, 9, 14, 19?
Answer: 5
2. nth term of 4, 9, 14, 19 (use 4+(n−1)×5).
Answer: 5n − 1
3. If nth term is 2n + 1, the 5th term is…
Answer: 11
4. If nth term is 2n + 1, the 1st term is…
Answer: 3
Touch practice
9 tap / typeTap an option or type the answer. Retry any miss. Extra generated questions appear after the set if this topic allows it.
Optional picture lab
After practiceReal world
Predict the next bill or score.
Connect
Functions: input n, output term.
⭐ Star quiz
9 questionsFinish the touch practice first if you can. Then answer without peeking. Read every “why”.