1.

If 9th term of an A.P. is zero, prove that its 29th term is double the 19th term.

Answer»

a9 = 0

a + (9 – 1)d =0

a + 8d = 0

a = - 8d …(i)

To Prove: a29 = 2a19

Proof: LHS= a29 = a + 28d = - 8d + 28d = 20d

RHS= 2a19 = 2[a + (18)d] = 2(- 8d + 18d) = 2(10d) = 20d

Since, LHS=RHS

Hence, proved



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