AlgebraUnit 2

Writing an explicit geometric sequence rule

An explicit rule gives a term without finding all previous terms.

  • An explicit rule gives a term without finding all previous terms.
  • When the first term is , use .

Example 1

Write an explicit rule for this sequence, starting at .

3, 6, 12, 24. \times2. \times2. \times2

Example 2

Write an explicit rule for this sequence, starting at .

32, 16, 8, 4. \times\frac{1}{2}. \times\frac{1}{2}. \times\frac{1}{2}

Remember
Always state whether the first term is or .

Your turn

5 practice questions
Question 1

Write an explicit rule for this sequence, starting at .

32, 16, 8, 4.
Check answer32, 16, 8, 4. \times\frac{1}{2}. \times\frac{1}{2}. \times\frac{1}{2}
Question 2

Write an explicit rule for this sequence, starting at .

135, 45, 15, 5.
Check answer135, 45, 15, 5. \times\frac{1}{3}. \times\frac{1}{3}. \times\frac{1}{3}
Question 3

Write an explicit rule for this sequence, starting at .

6, 12, 24, 48.
Check answer6, 12, 24, 48. \times2. \times2. \times2
Question 4

Write an explicit rule for this sequence, starting at .

7, 21, 63, 189.
Check answer7, 21, 63, 189. \times3. \times3. \times3
Question 5

Write an explicit rule for this sequence, starting at .

64, 32, 16, 8.
Check answer64, 32, 16, 8. \times\frac{1}{2}. \times\frac{1}{2}. \times\frac{1}{2}