SOLUTION: Find a1 and d for an arithmetic sequence with these terms: a4=9 and a7=18

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Question 852197: Find a1 and d for an arithmetic sequence with these terms: a4=9 and a7=18
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
a4=9 and a7=18
an = a1 + (n - 1)d
9 = a1 + 3d,
18 = a1 + 6d
a1 = 0, d = 3