Question

Dari barisan arimatika diketahu U7 = 22 dan U11 = 34. Jumlah 18 suku pertama adalah

Answer 1

Verified answer

Dik. Barisan deret aritmatika : U7= 22 & U11= 34
Dit. S18 ?

Jawab....

U7 = a + 6b = 22
U11 = a + 10b = 34
       ---------------------------     -
@ -4b = -12
@ b = 3

Suku pertama (a) :

a + 6b = 22
a + 6(3) = 22
a + 18 = 22
a = 22 - 18
a = 4

Sn = n/2 (2a + (n-1) b)
S18 = 18/2 (2(4) + (24-1) (3))
S18 = 9 ( 8 + (23) (3))
S18 = 9 ( 8 + 69 )
S18 = 9 (77)
S18 = 693

Semoga membantu... ^_^