Question

if the sum of first 7 terms of an AP is 49 and that of terms 17 terms is 289 ,find the sum of first n terms

Answer 1

=a+6d=49............ (1)
=a+16d=289........ (2)

subtracting 1 from to 2 we get
=10d=240
=d=24.
substitute value of d in equation 1
a+6*24=49
a+144=49
a=95
sum=n/2 (2a+(n-1)d)
=n/2 (190+24n-24)
=n/2 (166+24n)
=83n+12n^2.
pls mark as brainliest.

Answer 2

this is the right answer