Question

in an A.P if T1 =3,T2=5,then S3=?

Answer 1

a=3, a+d=5 then d=2 then S3=10

Answer 2

T1=3 t2=5 d=2 T3=7
Sn=n/2[2a+(n-1)d]
S3=3/2[6+(3-1)2]
S3=3/2[6+(2)2]
S3=3/2[6+4]
S3=3/2*10
S3=3*5
S3=15