In the formula $a_n = a_1 + (n-1)d$, why is the common difference $d$ multiplied by $(n-1)$ instead of $n$?

Because the common difference is added $n-1$ times to the first term.

Because the sequence must start at term number 0.

Because the first term $a_1$ is always 1.

Because $n$ represents the final value of the sequence.

3-5 Arithmetic Sequences Practice — Grade 9 math