Question

Jika suku ke-7 barisan aritmatika sama dengan 10 dan suku ke-13 sama dengan-2 , carilah tiga suku pertama barisan tersebut

Answer 1

U7 = 10 ⇒ a + 6b = 10
U13 = -2 ⇒ a + 12b = -2

a + 6b = 10
a + 12b = -2
2a + 12b = 20
a + 12 b = -2    -
a = 22

a + 6b = 10
22 + 6b = 10
6b = -12
b = -2

U1 = a = 22
U2 = a + b = 22 + (-2) = 20
U3 = a + 2b = 22 + 2(-2) = 18

Answer 2

U7 = 10
U13= -2
Un = a + (n-1)b
a + 9b = 10
a +12b = -2 -
      -3b  = 12
         b = -4
a+ 12 . -4 = 10
a + (-48) = 10
       a  = 58
U1 = 58
U2 = 58 -4 = 54
U3 = 58 - 8 = 50