Question

The first term of an arithmetic sequence is 12. The 9th term is -20. What is the common

difference of the arithmetic sequence?

Answer 1

-4

Explanation:

The formula of an arithmetic sequence is nth term=a+(n-1)d. First term is a and common difference is d.

Let's plug our info in.

-20=12+(9-1)d

-20=12+8d

Subtract 12 from both sides.

-32=8d

Divide both sides by 8.

d=-4

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