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Class 10 Mathematics Arithmetic Progressions (AP)Finding the sum of the first (n) terms of an APMedium

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Find the sum of the first (15) terms of the arithmetic progression (20,16,12,\ldots).

Answer and explanation

Correct answer: (-120)

The fifteenth term is (-36), so (S_{15}=\frac{15}{2}(20-36)=-120). In a decreasing progression, take (d) as negative.

Related tags

Decreasing Ap Negative Sum Ap Sum Finding The Sum Of The First (N) Terms Of An Ap Finding The Sum Of The First N Terms Of An Ap Arithmetic Progressions (Ap)Arithmetic Progressions Ap Mathematics

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