#1. Using your usual formulas, you have
10/2 (2a+9d) = 400
20/2 (2a+19d) - 400 = 1000
Now solve for a and d
#2. You know that
(x+4)-2x = (2x-7)-(x+4)
x = 15/2
If x=8, the three terms are 16,12,9
So S = a/(1-r) = 16/(1 - 3/4) = 64
In an arithmetic sequence the sum of the first ten terms is 400 and the sum of next ten terms is 1000. Find
The common difference
The first term
The first three terms of arithmetic sequence are also 2x, x+4 and 2x-7. Verify that when x = 8 the term form a geometric sequence and find the sum to infinity in this case.
S
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1 answer