SOLUTION: Find A1 and d for an arithmetic sequence with these terms: A4 = 9 A7 = 18

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Question 744976: Find A1 and d for an arithmetic sequence with these terms:
A4 = 9
A7 = 18
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
Only giving here two hints.

How many differences between A1 and A4? How many differences between A4 and A7?
Arithmetic Sequences depends on common difference between successive terms.