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Find the twentieth term of a sequence where the fifth term is −4 and the common difference is −2. Give the formula for the general term.

Short Answer

Expert verified

The twentieth term is -34 and the general term isan=−2n+6

Step by step solution

01

Step 1. Given Informaation. 

The fifth term is −4 and the common difference is −2.

02

Step 2. Find the first term by using the arithmetic formula. 

Substitute 5 for n,-2 for d, and the fifth term is -4, in the formula an=a1+n−1d.

a5=a1+5−1−2−4=a1−8a1=4

03

Step 3. Find the twentieth term.

Use the first term and the common difference to find the twentieth term.

a20=4+20−1−2=4−38=-34

04

Step 4. Find the general terms.

To find the general terms, substitute the first term 4 and the common difference -2 in the formula.

an=4+n−1−2=4−2n+2=−2n+6

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