Use a signed common difference
An arithmetic sequence adds the same signed amount at each step
- Difference Subtract earlier from later \(\displaystyle d=-2-(-7)=5\)
- Next term Add the difference \(\displaystyle -7+(-5)=-12\)
- Previous term Subtract the difference \(\displaystyle 4-(-3)=7\)
- Consecutive terms A gap of two indices contains two updates, not one
Worked example
The arithmetic sequence is 14, 8, 2, −4. Find the common difference and next term
- \(\displaystyle 8-14=-6\)Later minus earlier gives the signed difference
- \(\displaystyle 2-8=-6\)Check another pair
- \(\displaystyle -4+(-6)=-10\)Add the same difference to extend the sequence
Common mistakes
Difficulty levels
Questions about this topic
Can the common difference be zero?+
Yes. A constant sequence is arithmetic with difference zero
Can I use non-consecutive terms?+
Only if you account for the number of steps between them. The usual later-minus-earlier test uses consecutive terms
Is a previous term always smaller?+
No. In a decreasing arithmetic sequence, the previous term is larger
Can I use a calculator?+
A calculator is allowed unless a question is marked no calculator
Which year level and chapter is this?+
Year 11, VCE Units 1 & 2, General Mathematics, chapter 3: Sequences and finance