Question

Find the sum of first 25 sum of an AP, Nth term is given by n = 3n+2

Answer 1

n=3n+2
a1=3(1)+2
a1=5
in the same way by substituting n=2
a2=8
d=a2-a1
d=3
sn=n÷2(2a+(n-1)d)
s25=25÷2(2×5+(25-1)3)
s25=25÷2(82)
s25=25×41
s25=1025