Given that the sum of the first 20 terms of an arithmetic sequence is 1150 and the fifth term is twice the second term .

Question

find:

1.The first term and the common difference
2. find the general formula

Answer 1

term5 = a+4d
term2 = a+d

a+4d = 2(a+d)
a+4d = 2a + 2d
a = 2d

sum(20) = 10(2a + 19d) = 1150
2a + 19d = 115
4d+19d=115
23d = 115
d = 5
a = 10

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