Jumlah 20suku yang pertama dari barisan 1,3,5,7 adalah A200 B300 C400 D500

A = 1
b = 2

Sn = n/2 {2a + (n-1)b}
S20 = 20/2 {2.1 + (19).2}
S20 = 10 (2 + 38)
S20 = 10 (40)
S20 = 400

A = 1
b = 2

S20
= 20/2 (2(1) +(20-1)2
= 10(2+38)
= 10(40)
= 400