the 4th and 12th term are in the ration 1:3 and T 15 = 60 . Find AP

Asked by  | 8th Apr, 2012, 04:48: PM

Expert Answer:

We know that:
The general term of an A.P is given by:
an = a + (n-1)d, where a is the first term and d is the common difference.
 
Since, a4 : a12 = 1: 3
Solving this equation, we get 3a + 9d = a + 11 d which gives a = d
 
Also, it is given that T15 = 60
Thus, a + 14 d = 60
This gives, d = 4
Hence, a = d = 4
The required AP is
4, 8, 12, ...

Answered by  | 9th Apr, 2012, 04:48: PM

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