Tm=nTn=mShowTr=(m+n−r)Tm=a+(m−1)dn=a+(m−1)d→(i)Tn=a+(n−1)dm=a+(n−1)d→(ii)onsubstracting(i)from(ii)⇒(n−m)=(m−1−n+1)d⇒(n−m)=(m−n)d⇒d=−1,putd=−1equation(i)wegetn=a+(m−1)×−1⇒a=(m+n−1)⇒Tr=a+(r−1)d⇒Tr=(m+n−1)+(r−1)×−1⇒Tr=m+n−1r+1∴Tr=m+n−r
In an A. P., if mth is n and nth term is m, show that its rth term is (m +n -r).
If the mth term of an A.P. be 1n and nth term be 1m, then show that its (mn)th term is 1.