Question

Diketahui barisan aritmatika
1). 14,17,20,23,26,...
hitunglah :
a) U51 + U68 =
b) U147 - U67 =
sama caranya yaa​

Answer 1

Jawab:
(a.) U₅₁  + U₆₈ = 379
(b.) U₁₄₇ - U₆₇ = 240

Penjelasan:
Diketahui barisan aritmatika
{14, 17, ....}
{a,  U₂}
→  a = 14
beda = U₂-a = 17-14 = 3
→  b = 3

Rumus Un = a+b(n-1)

Ditanya
(a.) U₅₁       + U₆₈
= a+b(51-1) + a+b(68-1)
= a + 50b   + a+67b
= 2a + 50b + 67b
= 2a + 117b
= 2(14) + 117(3)
= 28 + 351
= 379

Ditanya
(b.) U₁₄₇        - U₆₇
= a+b(147-1)  -  (a+b(67-1))
= a+146b      -  (a+66b)
= a + 146b - a - 66b
= 146b - 66b
= 80b
= 80(3)
= 240

(xcvi)