the sum of first 7 terms of an ap is 49 and sum of the first 17 terms is 289 find the sum of first three terms
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Answer:
a7 = 49
a+6d= 49
a17= 289
a+16d= 289
from equation 1 and 2
a+16d-(a+6d) = 289-49
a+16d-a-6d= 240
10d=240
d=24
a+6d=49
a+6(24) =49
a=49- 144
a= find a
s3 = n/2 (2a+(n-1) d)
use n = 3
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