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

As a9 = o So, a + 8d = 0 a = -8d............ ...(i)Now , a29 = a + 28d a29 = -8d + 28da29 = 20d................(ii)a19 = a+ 18da19 = -8d + 18da19 = 10d.................(iii)Now from eq (ii) and (iii) 20d = 2* 10 da29 = 2*a19Hence proved......