Answer: choice B) a35 = -118
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Explanation:
When n = 5, an = 32 as shown in the first column of the table. This means the fifth term is 32. Plug in those values to get
an = a1+d(n-1)
32 = a1+d(5-1)
32 = a1+4d
Solve for a1 by subtracting 4d from both sides
a1 = 32-4d
We'll plug this in later
Turn to the second column of the table. We have n = 10 and an = 7. Plug those values into the formula
an = a1+d(n-1)
7 = a1 + d(10-1)
7 = a1+9d
Now substitute in the equation in which we solved for a1
7 = a1+9d
7 = 32-4d+9d ... replace a1 with 32-4d
7 = 32+5d
5d = 7-32
5d = -25
d = -25/5
d = -5
This tells us that we subtract 5 from each term to get the next term.
Use this d value to find a1
a1 = 32-4d
a1 = 32-4*(-5)
a1 = 32+20
a1 = 52
The first term is 52
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The nth term formula is therefore
an = 52 + (-5)(n-1)
which simplifies to
an = -5n + 57
To check this result, plug in n = 5 to find that a5 = 32. Similarly, you'll find that a10 = 7 after plugging in n = 10. I'll let you do these checks.
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Replace n with 35 to find the 35th term
an = -5n + 57
a35 = -5(35) + 57
a35 = -175 + 57
a35 = -118
