3+8+13+...+98=... Deret

Bab Barisan dan Deret
Matematika SMP Kelas IX

a = 3
b = 8 - 3 = 5

Un = a + (n - 1) b = 98
        3 + (n - 1) x 5 = 98
        (n - 1) x 5 = 98 - 3
        n - 1 = 95 / 5
        n = 19 + 1
         n = 20

Sn = n/2 x (a + Un)
S20 = 20/2 x (3 + 98)
       = 10 x 101
       = 1.010 

Matematika
Barisan dan deret IX SMP

Pembahasan :
Un = 98
a + (n - 1)b = 98
3 + (n - 1)(8 - 3) = 98
3 + (n - 1)5 = 98
3 + 5n - 5 = 98
5n - 2 = 98
5n = 100
n = 20

Sn = n/2(2a + (n - 1)b)
S20 = 20/2(2.3 + 19.5)
S20 = 10(6 + 95)
S20 = 10(101)
S20 = 1010