jumlah suku 35 yg pertama dari: 1+4+7+10+13...adalah

1,4,7...
a = 1
b = 4-1 = 3

Sn = (n/2)(a+Un)
S35 = (35/2)(1+U35)
S35 = (35/2)(1+a+[n-1]b)
S35 = (35/2)(1+1+[35-1]3)
S35 = (35/2)(2+102)
S35 = 35(52)
S35 = 1820

U35 =a + 34b = 1 + 34(3) = 1+102 = 103
S35 = n/2.(a+U35) = 35/2.(1+103) = 35/2.104 = 35.52 = 1820