**Here, **

a_{m} = n and

a_{n} = m

∴ a+(m-1)d = n and a+(n-1)d = m.**..(1)**

**Subtracting above two equation we get **

a +(m-1)d-a-(n-1)d=n-m

∴ md - d - nd + d = n-m

∴ d(m - n) = n - m

∴ d = -1

**Substituting d = -1 in a+(m-1)d = n we get **

∴ a+(m-1)(-1) = n

∴ a - m + 1 = n

∴ a = m +n - 1

**Now, **

p^{th} term is given by a_{p} = a+(p-1)d

= m+n-1+(p-1)(-1)

= m+n-1-p+1

= m + n - p