Sequences and Series 1 Question 4

4. If Tr is the r th term of an AP, for r=1,2,3,. . If for some positive integers m and n, we have Tm=1n and Tn=1m, then Tmn equals

(1998,2M)

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Answer:

Correct Answer: 4. (6)

Solution:

  1. Let

Tm=a+(m1)d=1nTn=a+(n1)d=1m

and

On subtracting Eq. (ii) from Eq. (i), we get

(mn)d=1n1m=mnmnd=1mn

Again, Tmn=a+(mn1)d=a+(mnn+n1)d

=a+(n1)d+(mnn)d=Tn+n(m1)1mn=1m+(m1)m=1



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