Two Step Rules

You'll learnto write the rule for a sequence that either adds a constant or multiplies by one.

Two sequences start at the same number. One adds 4 every step; the other multiplies by 2. For a moment they look like cousins — then one of them leaves the chart. This is the split the whole unit runs on: adding a constant, or multiplying by one. Watch the two rules diverge, and watch the off-by-one error that costs more points than either.

8 STEPS · 6 QUICK CHECKS · a_n = a₀ + dn · g_n = g₀ · rⁿ · v2

two step rules

Before you start

What you're looking at

Two sequences from the same start — one adding 4 each step, one doubling — with each term's position number labeled.

The question

Is the same amount being added each step, or the same factor multiplied?

Watch for

The count of steps from the first term to the one you want — the source of the n versus n−1 error.

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