Question

if a=12, an=240, d=2, find sn=?
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Answer 1

Step-by-step explanation:

an=a+(n-1)d

204=12+n-1×d

192= n-1×2

n=192/2+1

n=97

Sn=n/2(a+an)

=97/2(12+204)

=20952/2

Sn =10476