Question

1) deret aritmatika jika u6=65 u10=97 u15=?
2) tentukan jumlah 10 suku pertama dari deret 2+5+8+11...

Answer 1

A = 25 , b= 8 , U15= 137

Answer 2

Nomor 1
cari beda


cari suku awal
U6 = a +(6-1)b
U6 = a + 5b
65 = a + ( 5 x 8)
65 = a + 40
a = 65-40
a = 25

U15 = a +(15-1)b
U15 = a + 14b
U15 = 25 + (14 x 8)
U15 = 137

nomor 2
a (suku awal) = 2
beda (b) = 5-2 = 3

Sn = n/2 (2a+(n-1)b)
S10 = 10/2 [(2x2) + (10-1)3]
S10 = 5 (4 + (9 x 3))
S10 = 5 (4 + 27)
S10 = 5(31)
S10 = 155