Question

If the sum of the first m terms of an AP be n and the sum of its first
n terms be m then show that the sum of its first (m + n) terms is
-(m + n).
​

Answer 1

Step-by-step explanation:

sm=(2a+(m-1)d)m/2=n .......(1)

sn=2a+(n-1)d=m..........(2)

sm+n = m+n/2(2a+(m+n-1)d

if we find the value of d and a from 1 and 2

we get

sm+n= -(m+n)