Question

find the sum of series 6²+7²+8²+..........21²​

Answer 1

Answer:

6²+7²+8²+.........+21².

36+49+64+.........+441.

First term=a=36. (or) 6.

Common difference=d=a2-a1=49-36=13. (or) 7-6=1.

sn=n/2[2a+(n-1)d].

sn=441/2[2(36)+(441-1)(13)]. (or) 21/2[2(6)+(21-1)(1)].

=441/2[72+(440)(13)]. (or) 21/2[12+(20)(1)].

=441[36+5720]. (or) 21[6+20].

=441[5756]. (or) 21[26].

=2538396. (or) 546.

I think this is your answer.