Question

Tentukan rumus suku ke-n dari barisan aritmetika berikut ini , kemudian carilah suku ke-10 dan ke -17
a.3,8,13,18
b.4,7,10,13
c.125,115,105
d.6,-1,-8 .

Answer 1

1) 3,8,13,18
a = 3, b = 8-3=5

Un=a+(n-1)xb

maka:
U10= a+9b = 3+9x5 = 3+45 =48
U17= a+16b = 3+16x5 = 3+80 = 83

2) 4,7,10,13
a = 4, b = 7-4 = 3

U10= a+9b = 4+9x3 = 4+27 = 31
U17= a+16b = 4+16x3 = 4+48 = 52

3) 125,115,105
a=115 , b=115-125= -10

U10= a+9b = 115+9x(-10) = 115+(-90) = 35
U17= a+16b = 115+16x(-10) = 115+(-160)= -25

4) 6,-1,-8
a=6, b=-1-6=-7

U10=a+9b = 6+9x(-7) = 6+(-63) = -57
U17=a+16b = 6+16x(-7) =6+(-112) = -106