SOLUTION: First Question: Find the initial term of the arithmetic sequence with 10th term -1 and 20th term 7. (use initial term a0) Second Question: There are two geometric sequences w

Question 622864: First Question: Find the initial term of the arithmetic sequence with 10th term -1 and 20th term 7. (use initial term a0)

Second Question: There are two geometric sequences with 2nd term 5 and 4th term 80. What are the two possible values of the 3rd term?

I truly appreciate your help!!
Answer by MathTherapy(10552) (Show Source): You can put this solution on YOUR website!

Using the formula for an arithmetic sequence, we get:

----- Substituting 10 for n in formula

---- eq (i)

----- Substituting 20 for n in formula

------ eq (ii)

---- eq (i)
---- eq (ii)
- 10d = - 8 ------ Subtracting eq (ii) from eq (i)
d, or difference = , or

Since d = , then becomes: ----- Substituting 10 for n, and for d in formula

Initial term, or

=========
Check
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10th term

- 1 = - 1 (TRUE)

20th term

7 = 7 (TRUE)

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