Question

Sum of first fifften term of series 3+19+35+........is

Answer 1

a=3
d=19-3=16
n=15
now apply formula
sn=n/2[2a+(n-1)d]
sn=15/2[2×3+(15-1)16]
sn=15/2[6+14×16]
=15/2[6+224]
=15/2[230]
=15×115
=1725.

Answer 2

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