Question

Having a lot of trouble with this for some reason...

Find the 9th term of the arithmetic sequence.

a7= -42 and a11= -28

Answer 1

Its that flvs precal?

Answer 2

Looks like 3.5 is being added to get the subsequent terms

Answer 3

a7 = -42
a8 = -42 + 3.5
a9 = -42 + 3.5 + 3.5

Answer 4

ditto

Answer 5

Ah! Thank you so much @ParthKohli! So a9 would equal -35

Answer 6

Great, you can also use many formulas for problems like these. I have an alternative method to do this.

Answer 7

you'd just have to bear in mind that
to get the common ratio
from the 7th term to the 11th term, you'd need to use it 4 times

so \(\bf \textit{common ratio}=\cfrac{-28-(-42)}{4}\)

Answer 8

If you are given two terms, and want to calculate the middle term, take the average of the two terms.

Answer 9

In this problem, a9 happens to fall right in the middle of a7 and a11.

Answer 10

Thank you so much! The formula we were given to solve this an= a1+(n-1)d just was not making much sense to me.

Answer 11

You can use that one too! Actually, that is what we generally use for problems like these.

Answer 12

Do ask if you need the general way.