Find an equation for the nth term of the arithmetic sequence.

-20, -16, -12, -8, ...

Question

Find an equation for the nth term of the arithmetic sequence. 

-20, -16, -12, -8, ...

anonymous · Answer

Looks like an arithmetic series.

anonymous · Answer

$$
a_n = a_1 + (n-1)d
$$

anonymous · Answer

Like this:  an = -20 + 4(n - 1)

anonymous · Answer

That looks right.  Test it with $n=3$

anonymous · Answer

We know $n=3 \implies a_n=-12$

anonymous · Answer

don't you mean -16



























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anonymous · Answer

No, $-12$ is the third number in the series.

anonymous · Answer

Okay, you're right. Do mind helping me with one more question?

anonymous · Answer

If I have time.

anonymous · Answer

A certain species of tree grows an average of 0.5 cm per week. Write an equation for the sequence that represents the weekly height of this tree in centimeters if the measurements begin when the tree is 800 centimeters tall

anonymous · Answer

In this case $a_1 = 800$ and $d = 0.5$

anonymous · Answer

I know that's the formula, but for this it's quite difficult for me to input it.