# Arithmetic Sequences

In Zoom Math 200 and above, you can calculate the sum of an arithmetic sequence. For example, Zoom Math can calculate the answer to $1+3+5+…+99$. To type that problem, type it exactly the way it looks, including the three dots.

Zoom Math can’t do much else with arithmetic sequences, at least not directly. For example, if you want to know the 20th term in the sequence $1, 3, 5, …,$ Zoom Math can’t calculate that for you. It doesn’t know the formula.

Of course, Zoom Math is good with equations, so if you type in the formula yourself, Zoom Math can solve it for you. For arithmetic sequences, you can always use the formula $t=a+(n-1)d$, where $t$ is the term you want to calculate, $a$ is the first term of the sequence, $n$ is the number of the term you want to calculate, and $d$ is the difference between consecutive terms. For example, if you want to know the 20th term in the sequence 1, 3, 5, …, then $t$ is the answer you’re looking for, $a=1$, $n=20$, and $d=2$. I type these four equations into Zoom Math:

a = 1

n = 20

d = 2

t = a+(n-1)d

And Zoom Math gives me the correct answer $t=39$.