Question

Hitunglah jumlah 40 suku aritmatika dari deret aritmatika 3+8+13+…

Answer 1

Sn= n/2 (2a + (n-1) . b)
s40= 40/2 (2.3 + (40-1) . 5)
s40= 20 (6 + (39 .5)
s40= 20 (6+ 195)
s40= 20.211
s40= 422

Answer 2

S40 = n/2 ( 2a + (n - 1 ) b)
a = 3 b = 5 n = 40
s40 = 40/2 ( 2.3 + 39.5)
      = 40/2 ( 201 )
      = 8040 /2
      = 4020