Which term of the AP : 21, 18, 15,... is ` -81`? Also, is any term 0? Give reason for your answer.

Explanation

Here, `a = 21, d = 18 – 21 = – 3 `


and `a_n = – 81,`
and we have to find n.


As `a_n = a + ( n – 1) d,`


we have `– 81 = 21 + (n – 1)(– 3)`
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