Question

Barisan aritmatika:
u5=8 dan u11=26
tentukan: a) un=
b) u125=

Answer 1

U11 ⇒  a + 10b = 26
U 5  ⇒  a +  4b = 8  _
                   6b = 18
                     b = 18/6
                     b = 3
subtitusikan
a +4b =8
  a = 8 - 4b
  a = 8 -4(3)
  a = 8 - 12
  a = - 4
tentukan rumus
Un = a + ( n-1) b
     = -4 ( n- 1) 3
     = -4 + 3n - 3
     = -7 + 3n
tentukan U125
u125 = -7 + 3(125)
       = -7 + 375
       = 368

Answer 2

U5 = a + 4b = 8
U11 = a + 10b = 26
---------------------------(-)
-6b = -18
b = 3
a + 4b = 8
3 + 4b = 8
4b = 8 - 3 = 5
b = 5/4
Un = a + (n - 1)b
= 3 + (n - 1) 5/4
= 3 + 5/4 n - 5/4 ---> ×4
= 12 + 5n - 5
= 5n + 7
U125 = 5n + 7
= 5.125 + 7
= 632