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How many term of the A.P. 15 , 12, 9 ., ...

How many term of the A.P. 15 , 12, 9 ., - are needed to give the sum 15 ? Explain the duble answer .

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n = 1 or 10
Sum of the terms from ` 2^(nd) " to" 9^(th)` term is zero .
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