Problem

Problem

The interval in which f(x)=3cos⁡4x+10cos⁡3x+6cos⁡2x−3f(x) = 3\cos^4 x + 10\cos^3 x + 6\cos^2 x - 3 increase or decrease in (0,π)(0, \pi) a. decreases on (π2,2π3)\left(\frac{\pi}{2}, \frac{2\pi}{3}\right) and increases on (0,π2)∪(2π3,π)\left(0, \frac{\pi}{2}\right) \cup \left(\frac{2\pi}{3}, \pi\right) b. decreases on (π2,π)\left(\frac{\pi}{2}, \pi\right) and increases on (0,π2)\left(0, \frac{\pi}{2}\right) c. decreases on (0,π2)∪(2π3,π)\left(0, \frac{\pi}{2}\right) \cup \left(\frac{2\pi}{3}, \pi\right) and increases on (π2,2π3)\left(\frac{\pi}{2}, \frac{2\pi}{3}\right) d. decreases on (0,π2)\left(0, \frac{\pi}{2}\right) and increases on (π2,π)\left(\frac{\pi}{2}, \pi\right)

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