Question

If the 8th term of an AP is zero prove that its 38th term is triple its 18th term

Answer 1

May this will help you

Answer 2

we have a+7d =0 ........................(1)

We have to prove a+37d = 3(a+17d)
 
  LHS = a+37d = a+7d + 30d         
                        = 0+30d             [By (1)]
                        = 30d

RHS = 3(a+17d)
         = 3(a+7d+10d)                    
         = 3(0+10d)                      [By (1)]
         = 30d
So, LHS = RHS                               
                                                     hence proved.