If are in A.P., then is quadratic in ‘’. If are in A.P., then is cubic in

Case II:

If are not in A.P., but in G.P., then , where is the common ratio of the G.P. and Again, ifare not in G.P. but are in G.P., then is of form and is the common ratio of the G.P. and

The sum of 20 terms of the series is

a)

4010

b)

3860

c)

4240

d)

None of these

Question ID - 51133 | Toppr Answer

Let be the terms of a sequence and let

Case I:

If are in A.P., then is quadratic in ‘’. If are in A.P., then is cubic in

Case II:

If are not in A.P., but in G.P., then , where is the common ratio of the G.P. and Again, ifare not in G.P. but are in G.P., then is of form and is the common ratio of the G.P. and