If the sum of first 7 terms of an AP is 49 and that of 17 terms is 289, find the sum of first n terms.
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a=49
d=289-49=240
n=?
an=289
an =a+(n-1)d
289=49+(n-1)240
289=49+240n-240
289+240=49+240n
529=49+240n
529-49=240n
480=240n
n=480/240
n=22/11
d=289-49=240
n=?
an=289
an =a+(n-1)d
289=49+(n-1)240
289=49+240n-240
289+240=49+240n
529=49+240n
529-49=240n
480=240n
n=480/240
n=22/11
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