The first four terms of an arithmetic sequence are

Question

2, x-y, 2x+y+7 and x-3y where x and y are constants.

Find the x and y and hence find the sum of the first 30 terms.

Answer 1

(2x+y+7) - (x-y) = (x-y)-2
(x-3y)-(2x+y+7) = (x-y)-2

x=2, y=-3

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