Question

Bantuiin no 7,8,9.pliss.

Answer 1

nomor 7
Un = a + (n-1) b,
maka
U5 = a + (5-1) b = 8 -> a + 4b = 8
U9 = a + (9-1) b = 20 -> a + 8b = 20

eliminasi:
a + 4b = 8
a + 8b = 20 -
   -4b = -12
     b = 3

substitusi:
a + 4b = 8
a + 4 (3) = 8
a + 12 = 8
a = 8 - 12
a = -4

U10 = a + (10-1) b
      = -4 + 9 (3)
     = -4 + 27
     = 23
nomor 8
U3 = 18 berarti a + (3-1) b = 18 -> a + 2b = 18
U7 = 38 berarti a + (7-1) b = 38 -> a + 6b = 38

eliminasi
a + 2b = 18
a + 6b = 38 -
-4b = -20
  b = 5

substitusi
a + 2b = 18
a + 2(5) = 18
a + 10 = 18
a = 18 - 10
a = 8

U24 = a + (24-1) b
     = 8 + 23 (5)
     = 8 + 115
     = 123
jadi
Sn = n/2 (a + Un)
S24 =  24/2 (8 + 123)
       = 12 (131)
        = 1572

nomor 9
U1 = 20, dimana U1 sama saja dengan a, maka a = 20
U2 = 23
dan bertambah 3 setiap baris kebelakang

Un = a + (n - 1) b

U2 = 20 + (2 - 1) b
23 = 20 + 1 b
23 - 20 = b
b = 3

U20 = 20 + (20 - 1) 3
     = 20 + 19 (3)
     = 20 + 57
     = 77
maka
Sn = n/2 (a + Un)
S20 = 20/2 (20 + 77)
     = 10 (97)
      = 970

Answer 2

No 9 = 1030 aku kerjain pake rumus n hitung 1 per 1 jwabannya ttp 1030