Which term of the A.P. :21,18,15..............is zero?

1.	Which term of the A.P. :21,18,15..............is zero?
Answer» The given AP is21,18,15......................,0Here a=21 and d=18-21= -3 and an=0,n=?{tex}\\Rightarrow{/tex}\xa0an\xa0= a + (n - 1)d{tex}\\Rightarrow{/tex}\xa00 = a + (n - 1)dNow on substitution of value of a and d we get\xa00 = 21 + (n - 1) (-3)-21 =(n-1)(-3)\xa0n - 1 =\xa0{tex}\\frac{{ - 21}}{{ - 3}}{/tex}\xa0n - 1 = 7Hence n = 8.

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