Question

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Q---If 9th term of an AP is zero , Prove that its 29th term is double of its 19th term?

Answer 1

Given :- a9 = 0

To find nth term :-

an = a + ( n - 1 )d

9th term is :-

a + 8d = 0

a = ( - 8d ) .... ( i )

To prove :- a29 = 2 ( a19 )

LHS :-

it's 29th term is :-

a + 28d

= - 8d + 28d ... ( from i )

= 20d

RHS :-

• 2 ( a 19 )

2 ( a + 18d )

= 2 ( - 8d + 18d ) .. .. ( from i )

= 2 ( 10d )

= 20d


Since , LHS = RHS

hence proved !!