Question

tell me the formula for find this numerical​

Answer 1

you can use the formula
Sn=n/2[2a+(n-1)d
or
Sn=n/2[a+tn]
and to find the value of 'n'
you have to use the formula
tn=a+(n-1)d

Answer 2

the formula is n(n+1) (2n+1)/6

here n is 30

30(31) 61/6

the answer is 9455

option b

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