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Find the first term and common difference of the sequence with the given terms. Give the formula for the general term.

The third term is −13 and the seventeenth term is 15.

Short Answer

Expert verified

The first term, common difference, and the general formula are -17, 2, andan=2n−19.

Step by step solution

01

Step 1. Given Information.

The third term is −13 and the seventeenth term is 15.

02

Step 2. Write the equation for the third and seventeenth terms.

Use the arithmetic sequence formula as we have a3=−13and a17=15.

a3=a1+3−1d−13=a1+2da1=−13−2d(1)

And,

role="math" localid="1645376363200" a17=a1+17−1d15=a1+16da1=15−16(2)

03

Step 3. Find the value of common difference d. 

Put equations 1 and 2 equal to find d.

−13−2d=15−16d16d−2d=15+1314d=28d=2

04

Step 4. Find the value of the first term.

Substitute 2 for d in equation 1.

a1=−13−22=-17

05

Step 5. Find the general term. 

Substitute -17 for the first term and 2 for d in the arithmetic formula.

a1=−17+n−12=−17+2n−2=2n−19

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