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y=6x-12 cos x,x in[-(pi)/(2);pi]

y=6x12cosx,x[π2;π] y=6 x-12 \cos x, x \in\left[-\frac{\pi}{2} ; \pi\right]

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Q. y=6x12cosx,x[π2;π] y=6 x-12 \cos x, x \in\left[-\frac{\pi}{2} ; \pi\right]
  1. Calculate derivative and critical points: Calculate the derivative of yy to find critical points.y=6x12cosxy = 6x - 12 \cos xdydx=6+12sinx\frac{dy}{dx} = 6 + 12 \sin xSet dydx=0\frac{dy}{dx} = 0 to find critical points:6+12sinx=06 + 12 \sin x = 0sinx=12\sin x = -\frac{1}{2}
  2. Solve for x: Solve sinx=12\sin x = -\frac{1}{2} for xx in the interval [π2,π][-\frac{\pi}{2}, \pi].\newlinex=π6,7π6x = -\frac{\pi}{6}, \frac{7\pi}{6}\newlineBut 7π6\frac{7\pi}{6} is not in the interval [π2,π][-\frac{\pi}{2}, \pi].\newlineSo, the critical point is x=π6x = -\frac{\pi}{6}.
  3. Calculate second derivative: Calculate the second derivative to determine the nature of the critical point.\newlined2ydx2=12cosx\frac{d^2y}{dx^2} = 12 \cos x\newlineEvaluate d2ydx2\frac{d^2y}{dx^2} at x=π6x = -\frac{\pi}{6}:\newlined2ydx2=12cos(π6)=12×(3/2)=63\frac{d^2y}{dx^2} = 12 \cos(-\frac{\pi}{6}) = 12 \times (\sqrt{3}/2) = 6\sqrt{3}\newlineSince 6\sqrt{3} > 0, the function has a relative minimum at x=π6x = -\frac{\pi}{6}.

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