Question

find s10 of 3+5+7+9​

Answer 1

n/2(2a+(n-1)d)

10/2(2(3)+(10-1)2)

5(6+(9)2)

5(6+18)

5(24)

120

Answer 2

Here, n=10

a=3

D=2

NOW, an=a+(n-1)×d

an=3+(10-1)2

an=21

Now,

Sn= n/2×(an +a)

S10=10/2×(21+3)

S10=5×24

S10=120