Suatu deret geometri diketahui U2 = 40, U5 = 5. tentukansuku ke-8 dan jumlah 5suku pertama
Jawaban Terkonfirmasi
U2 = 40
ar = 40
U5 = 5
ar^4 = 5
ar^4 / ar = 5/40
r^3 = 1/8
r = 1/2
ar = 40
a (1/2) = 40
a = 80
U8 = ar^7
U8 = 80 (1/2)^7
U8 = 80/128
U8 = 5/8
S5 = a (1 – r^n) / 1 – r
S5 = 80 (1 – (1/2)^5) / 1 – 1/2
S5 = 80 (1 – (1/32) / 1/2
S5 = 160 (1 – 1/32)
S5 = 160 – 5
S5 = 155