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

1.	If 9th term of A.P. is zero, prove that its 29th term is double of its 19th term.
Answer» a+(9-1)d=0 ; a+8d=0 ; a= -8d a19=a+(19-1)d ; a+18d. -8d+18d= 10d. Similarly, a29=a+(29-1)d ; a+28d. -8d+28d= 20d. So, 20d is double of 10d.........Is it correct???????

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