For an ap if tm =1/n and tn=1/m then a-d=
let a be the first term and d be the common difference of an AP series
tm = a+ (m-1)d =1/n ….(i) (given)
tn = a+(n-1)d=1/m …...(ii) (given)
Subtracting equation (ii) from (i)
d[(m-1)-(n-1)] = 1/n -1/m,
d(m-n) = (m-n)/mn,
d = 1/mn ….(iii)
Substituting equation (iii) in (i)
a+(m-1)/mn = 1/n,
a = 1/n[1-(m-1)/m],
a = 1/mn ….(iv)
Hence a-d = 1/mn - 1/mn = 0 Ans.