SOLUTION: the first three terms of an arithmetic projection are x,2x+1 and 5x+1.find x and the sum of the first 10 terms
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Question 1110915: the first three terms of an arithmetic projection are x,2x+1 and 5x+1.find x and the sum of the first 10 terms Answer by ikleyn(52787) (Show Source):
(2x+1) -x = (5x+1) - (2x+1) (<<<---=== - = - )
x + 1 = 3x
1 = 2x ====> x = is the first term.
(2x+1) - x = (1+1) - 1/2 = is the common difference.
The 10-th term is + = = 14.
The sum of 10 terms = the average of the 1-st and the 10-th terms (which is equal to = 7.25), taken 10 times:
Sum = 7.25*10 = 72.5.
