Question

Suku ke 4 barisan aritmatika adalah 19 dan suku ke 7 adalah 31.tentukan suku ke 50

Answer 1

U4 = a+3b = 19 ---> a=19-3b
u7 = a+6b = 31
a+6b = 31
19-3b+6b = 31
3b = 31-19
3b = 12
b = 4
a = 19-3b
a = 19-3(4)
a = 19-12
a = 7

u50 = a+49b
u50 = 7+49(4)
u50 = 7+196
u50 = 203

Answer 2

Un = a+(n-1)b
U4 = a+(4-1)b
19 = a+3b

Un = a+(n-1)b
U7 = a+(7-1)b
31 = a+6b

a+3b = 19
a+6b = 31
dikurangi
-3b = -12
b = 4

a+3b = 19
a+3(4) = 19
a+12 = 19
a =19-12
a = 7

Un = a+(n-1)b
U50 = 7+(50-1)4
U50 = 7+(49)4
U50 = 7+196
U50 = 203