The problem asks to sketch the graph of the function $y = x\sqrt{4 - x^2}$.

AnalysisCalculusFunction AnalysisDerivativesGraphingDomainCritical PointsLocal Maxima/MinimaOdd Functions
2025/7/3

1. Problem Description

The problem asks to sketch the graph of the function y=x4x2y = x\sqrt{4 - x^2}.

2. Solution Steps

First, we determine the domain of the function. Since we have a square root, we must have 4x204 - x^2 \ge 0, which means x24x^2 \le 4, or 2x2-2 \le x \le 2. Therefore, the domain of the function is [2,2][-2, 2].
Next, we find the derivative of the function with respect to xx:
y=x4x2y = x\sqrt{4 - x^2}
Using the product rule, we have:
dydx=4x2+x124x2(2x)=4x2x24x2\frac{dy}{dx} = \sqrt{4 - x^2} + x \cdot \frac{1}{2\sqrt{4 - x^2}} \cdot (-2x) = \sqrt{4 - x^2} - \frac{x^2}{\sqrt{4 - x^2}}
dydx=4x2x24x2=42x24x2\frac{dy}{dx} = \frac{4 - x^2 - x^2}{\sqrt{4 - x^2}} = \frac{4 - 2x^2}{\sqrt{4 - x^2}}
To find the critical points, we set dydx=0\frac{dy}{dx} = 0:
42x24x2=0\frac{4 - 2x^2}{\sqrt{4 - x^2}} = 0
42x2=04 - 2x^2 = 0
2x2=42x^2 = 4
x2=2x^2 = 2
x=±2x = \pm\sqrt{2}
Since both values are within the domain [2,2][-2, 2], they are both critical points.
Now, we determine the sign of dydx\frac{dy}{dx} in the intervals [2,2)[-2, -\sqrt{2}), (2,2)(-\sqrt{2}, \sqrt{2}), and (2,2](\sqrt{2}, 2].
- For x[2,2)x \in [-2, -\sqrt{2}), say x=1.5x = -1.5, we have dydx=42(2.25)42.25=44.51.75=0.51.75<0\frac{dy}{dx} = \frac{4 - 2(2.25)}{\sqrt{4 - 2.25}} = \frac{4 - 4.5}{\sqrt{1.75}} = \frac{-0.5}{\sqrt{1.75}} < 0.
- For x(2,2)x \in (-\sqrt{2}, \sqrt{2}), say x=0x = 0, we have dydx=404=42=2>0\frac{dy}{dx} = \frac{4 - 0}{\sqrt{4}} = \frac{4}{2} = 2 > 0.
- For x(2,2]x \in (\sqrt{2}, 2], say x=1.5x = 1.5, we have dydx=42(2.25)42.25=44.51.75=0.51.75<0\frac{dy}{dx} = \frac{4 - 2(2.25)}{\sqrt{4 - 2.25}} = \frac{4 - 4.5}{\sqrt{1.75}} = \frac{-0.5}{\sqrt{1.75}} < 0.
So, the function is decreasing on [2,2)[-2, -\sqrt{2}), increasing on (2,2)(-\sqrt{2}, \sqrt{2}), and decreasing on (2,2](\sqrt{2}, 2].
This means that there is a local minimum at x=2x = -\sqrt{2} and a local maximum at x=2x = \sqrt{2}.
Let us find the y-values at these points.
- When x=2x = -\sqrt{2}, y=24(2)2=242=22=2y = -\sqrt{2} \sqrt{4 - (-\sqrt{2})^2} = -\sqrt{2} \sqrt{4 - 2} = -\sqrt{2} \sqrt{2} = -2.
- When x=2x = \sqrt{2}, y=24(2)2=242=22=2y = \sqrt{2} \sqrt{4 - (\sqrt{2})^2} = \sqrt{2} \sqrt{4 - 2} = \sqrt{2} \sqrt{2} = 2.
At the endpoints of the domain, x=2x = -2 and x=2x = 2, we have y=0y = 0.
- When x=2x = -2, y=24(2)2=20=0y = -2 \sqrt{4 - (-2)^2} = -2 \sqrt{0} = 0.
- When x=2x = 2, y=24(2)2=20=0y = 2 \sqrt{4 - (2)^2} = 2 \sqrt{0} = 0.
The function is odd since y(x)=(x)4(x)2=x4x2=y(x)y(-x) = (-x) \sqrt{4 - (-x)^2} = -x \sqrt{4 - x^2} = -y(x). Therefore the graph is symmetric with respect to the origin.

3. Final Answer

The graph is a curve that passes through (2,0)(-2, 0), (2,2)(-\sqrt{2}, -2), (0,0)(0, 0), (2,2)(\sqrt{2}, 2), and (2,0)(2, 0). There is a local minimum at (2,2)(-\sqrt{2}, -2) and a local maximum at (2,2)(\sqrt{2}, 2). The function is odd, and the domain is [2,2][-2, 2]. The curve increases from x=2x=-2 to x=2x=-\sqrt{2}, decreases from x=2x=-\sqrt{2} to x=0x=0 and x=0x=0 to x=2x=\sqrt{2}, increases from x=0x=0 to x=2x=\sqrt{2} and decreases from x=2x=\sqrt{2} to x=2x=2.
The graph looks like a sideways figure-eight.
Final Answer: (Sketch of the graph is required for the actual answer)

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