Explanation:
Calcute the ratio :
r = Un/Un-1
r = 60/120
r = ½
Calculate 4th term :
Un = ar^n-1
U4 = 120 × ½^4-1
U4 = 120 × ½³
U4 = 120 × 0.125
U4 = 15
Calculate 5th term :
U5 = 120 × ½^5-1
U5 = 120 × ½⁴
U5 = 120 × 0.0625
U5 = 7.5
Calculate 6th term :
U6 = 120 × ½^6-1
U6 = 120 × ½⁵
U6 = 120 × 0.03125
U6 = 3.75
given :
120, 60, 30, _, _, _
find r!
solution :
r = 60/120 = ½.
=> 120,60,30, 15, 15/2 , 15/4 , ...
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