Question

Dari deret aritmatika diketahui Sn = 93,5, a=1, U2= 2,5. Hituglah n dan Un !

Answer 1

Verified answer

Deret Aritmatika

Sn = 93,5
a = 1
U2 = 2,5

b = U2 - a = 2,5 - 1 = 1,5

Un = a + (n - 1)b
Un = 1 + 1,5n - 1,5)
Un = 1,5n - 0,5

Sn = n/2 (a + Un)
93,5 = n/2 (1 + (1,5n - 0,5)
93,5 = n/2 (1/2 + 3/2 n)
93,5 = n/4 + 3/4 n²
Kedua ruas kalikan 4
374 = 3n² + n

3n² + n - 374 = 0
(3n + 34)(n - 11) = 0

n yg memenuhi :
n = 11

Un = U11 = a + 10b
U11 = 1 + 10 . 3/2
U11 = 1 + 15
U11 = 16