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

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

Posted by Om Khobragade 6 years, 6 months ago

CBSE > Class 10 > Mathematics

1 answers

Sia ? 6 years, 6 months ago

The given AP is
21,18,15......................,0
Here a=21 and d=18-21= -3 and a_n=0,n=?
{tex}\Rightarrow{/tex} a_n = a + (n - 1)d
{tex}\Rightarrow{/tex} 0 = a + (n - 1)d

Now on substitution of value of a and d we get
0 = 21 + (n - 1) (-3)

-21 =(n-1)(-3)
n - 1 = {tex}\frac{{ - 21}}{{ - 3}}{/tex}
n - 1 = 7
Hence n = 8.

0Thank You

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