SOLUTION: Find the 1st term of the arithmetic sequence with 11th term −1 and 21th term 7.

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Question 927791: Find the 1st term of the arithmetic sequence with 11th term −1 and 21th term 7.
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39618)   (Show Source): You can put this solution on YOUR website!
Use the formulas.
d, common difference
n, term index
a, first term .
.
Use this formula and make two linear equations in the variables, a and d.
Answer by MathTherapy(10552)   (Show Source): You can put this solution on YOUR website!

Find the 1st term of the arithmetic sequence with 11th term −1 and 21th term 7.


 



______ ---------- eq (i)









 ------- eq (ii) 

 ------- Substituting  for d in eq (ii)



 





Term 1 or , or  

You can do the check!! 

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