Tenrukan jumlah bilangan ganjil berikut! A.1+3+5+7+.... Sampai 20 suku B.sembilan belas bilangan ganjil pertama

Sn = 1/2 . n (U1+Un)

a. n = 20, U1 = 1, Un = 1 + (20-1)2
Un = 1 + 19(2) = 1 + 38 = 39

Sn = 1/2 . n . (U1 + Un)
S20 = 1/2 . 20 . (1 + 39)
S20 = 10 . 40
S20 = 400

b. n = 19, U1 = 1, Un = 1+(19-1)2
Un = 1+ 18(2) = 1 + 36 = 37

Sn = 1/2 . n . (U1+Un)
S19 = 1/2 . 19 . (1+37)
S19 = 1/2 . 38 . 19
S19 = 19 . 19
S19 = 361