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91Ó°ÊÓ

In the following exercises, 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 −26and the sixteenth term is −91.

Short Answer

Expert verified

The first term is -16and the common difference is -5.

The general term is an=-5n-11.

Step by step solution

01

Step 1. Given Information 

We are given that the third term is −26and the sixteenth term is −91.

We have to find the first term and common difference of a sequence.

02

Step 2. Finding the first term and common difference 

Let aa be the first term and dbe the common difference, so

a3=-26a+(3-1)d=-26a+2d=-26-(1)

Similarly, sixteenth term is given by,

a16=-91a+(16-1)d=-91a+15d=-91-(2)

03

Step 3. Solving the equations

Subtracting the second and first equation, we get

a-a+15d-2d=-91-(-26)13d=-91+2613d=-65d=-6513d=-5

Now, putting the value of din first equation, we get

a+2(-5)=-26a-10=-26a=-26+10a=-16

04

Step 4. Finding the general term 

Now, putting the value of first term and common difference in an=a1+(n-1)d,

an=-16+(n-1)(-5)an=-16-5n+5an=-5n-11

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