Understanding the Linear Pattern: Solving for f(n) = 15 at f(1) = 15, f(2) = 30, f(3) = 45, f(4) = 60

When examining a sequence of ordered pairs such as:

  • f(1) = 15
  • f(2) = 30
  • f(3) = 45
  • f(4) = 60

Understanding the Context

we notice a clear arithmetic progression: each term increases by 15 as the input increases by 1. This strong linear pattern suggests that the function f(n) is linear in nature, describable by a simple equation of the form:
f(n) = an + b, where a is the slope and b is the y-intercept.


Step 1: Confirming the Linear Relationship

Let’s plug in values to find a and b.

Using f(1) = 15:
 a(1) + b = 15 → a + b = 15  (1)

Key Insights

Using f(2) = 30:
 a(2) + b = 30 → 2a + b = 30  (2)

Subtract (1) from (2):
 (2a + b) − (a + b) = 30 − 15
 a = 15

Substitute a = 15 into (1):
 15 + b = 15 → b = 0

Thus, the function is:
f(n) = 15n

Check with all points:

  • f(1) = 15×1 = 15
  • f(2) = 15×2 = 30
  • f(3) = 15×3 = 45
  • f(4) = 15×4 = 60

Final Thoughts

✓ Confirmed—this linear model fits perfectly.


Step 2: Real-World Meaning Behind the Pattern

Functions like f(n) = 15n model proportional growth, where the output increases steadily with the input. In practical terms, if f(n) represents a total value accumulating per time unit, then:

  • After 1 unit: $15
  • After 2 units: $30
  • After 3 units: $45
  • After 4 units: $60

This could represent an increasing bonus per hour, escalating rewards, or cumulative payments growing linearly with time.


Step 3: Predicting Future Values

Using the formula f(n) = 15n, you can easily compute future outputs:

  • f(5) = 15×5 = $75
  • f(6) = 15×6 = $90

This predictable growth makes linear functions ideal for modeling steady, consistent change.


Step 4: Alternative Representations

Though f(n) = 15n is the simplest form, the same sequence can also be expressed using recursive definitions:

  • Recursive form:
     f(1) = 15
     f(n) = f(n−1) + 15 for n > 1

This recursive pattern mirrors the additive growth visible in the table.