Jawabanmu

2014-03-19T12:44:21+07:00
Sn =  n^{2} + 5n
S20 =  20^{2} + ( 5 x 20 )
S20 = 400 + 100
S20 = 500

semoga bisa membantu dan mohon koreksi jika salah :)
2014-03-19T13:11:05+07:00
Sn = + 5n
S20 = + ( 5 x 20 )
S20 = 400 + 100
S20 = 500

semoga saja benar :)