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If \(f(x) = \cos\left\{\dfrac{\pi}{3}[x] + x\right\}\) for \(1 < x < 2\), where \([\cdot]\) is the greatest integer function, then what is \(f\left(\dfrac{\pi}{2}\right)\) equal to?

This question was previously asked in
NDA 2 2026 GAT Question Paper (13-Sep-2026)
The correct answer is

\(-\dfrac{\sqrt{3}}{2}\)

Since \(\dfrac{\pi}{2}\) lies between \(1\) and \(2\), \(\left[\dfrac{\pi}{2}\right] = 1\), so \(f(x) = \cos\left(\dfrac{\pi}{3} + x\right)\) on this interval. Thus \(f\left(\dfrac{\pi}{2}\right) = \cos\left(\dfrac{\pi}{3} + \dfrac{\pi}{2}\right) = \cos\left(\dfrac{5\pi}{6}\right) = -\dfrac{\sqrt{3}}{2}\).

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