SOLUTION: find the formula for a_n if a_1 = -4 and a

SOLUTION: find the formula for a_n if a_1 = -4 and a_5 = 16. This is AP

Question 1087018: find the formula for a_n if a_1 = -4 and a_5 = 16. This is AP
Answer by ikleyn(52778) (Show Source): You can put this solution on YOUR website!
.

 =  = -4 + 4*d = 16  ====>  4d = 20  ===>  d = 5.


The formula is  = -4 + 5*(n-1) = -4 +5n - 5 = -9 + 5n,  n = 1, 2, 3, . . . 


Answer. The general formula is   = -4 + 5*(n-1)  or  (which is the same)   =  -9 + 5n,  n = 1, 2, 3, . . .

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