Mathematics

Mathematics

Problem

Let h(x)=sin⁡(kx)h(x)=\sin(kx) be defined on [0,π][0,\pi]. What is the smallest positive integer kk for which the average value of hh on [0,π][0,\pi] equals 0? a) k=1k=1 b) k=4k=4 c) k=2k=2 d) k=3k=3
Intuitive explanation

The average value of a function on an interval is found by integrating it and dividing by the interval's length. For sin⁡(kx)\sin(kx) on [0,π][0,\pi], you need the integral ∫0πsin⁡(kx) dx\int_0^\pi \sin(kx)\,dx to equal zero—meaning the positive and negative areas cancel out perfectly. This happens when the sine wave completes enough full cycles (or half-cycles) within the interval so that symmetry forces cancellation. Find the smallest kk where this balance occurs.

Intuitive explanation

The average value of a function on an interval is found by integrating it and dividing by the interval's length. For sin⁡(kx)\sin(kx) on [0,π][0,\pi], you need the integral ∫0πsin⁡(kx) dx\int_0^\pi \sin(kx)\,dx to equal zero—meaning the positive and negative areas cancel out perfectly. This happens when the sine wave completes enough full cycles (or half-cycles) within the interval so that symmetry forces cancellation. Find the smallest kk where this balance occurs.

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