Rectangle Perimeter
1. **Problem 1: Find the dimensions of a rectangle with area 1000 m² that minimize the perimeter.**
2. Given:
- Area $A = xy = 1000$
- Perimeter $P = 2x + 2y$
3. Express $y$ in terms of $x$ using the area constraint:
$$y = \frac{1000}{x}$$
4. Substitute into the perimeter formula:
$$P(x) = 2x + 2\frac{1000}{x} = 2x + \frac{2000}{x}$$
5. To minimize $P(x)$, find the derivative and set it to zero:
$$P'(x) = 2 - \frac{2000}{x^2} = 0$$
6. Solve for $x$:
$$2 = \frac{2000}{x^2} \implies 2x^2 = 2000 \implies x^2 = 1000 \implies x = \sqrt{1000} = 10\sqrt{10} \approx 31.62$$
7. Find $y$:
$$y = \frac{1000}{31.62} \approx 31.62$$
8. So, the rectangle is a square with dimensions approximately $31.62, 31.62$ meters.
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1. **Problem 2: Find the point on the line $y = 5x + 3$ closest to the origin.**
2. The distance squared from origin to point $(x,y)$ is:
$$D^2 = x^2 + y^2$$
3. Substitute $y = 5x + 3$:
$$D^2 = x^2 + (5x + 3)^2 = x^2 + 25x^2 + 30x + 9 = 26x^2 + 30x + 9$$
4. Minimize $D^2$ by taking derivative and setting to zero:
$$\frac{d}{dx}D^2 = 52x + 30 = 0 \implies x = -\frac{30}{52} = -\frac{15}{26}$$
5. Find $y$:
$$y = 5\left(-\frac{15}{26}\right) + 3 = -\frac{75}{26} + \frac{78}{26} = \frac{3}{26}$$
6. The closest point is $\left(-\frac{15}{26}, \frac{3}{26}\right)$.
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**Final answers:**
- Rectangle dimensions: $31.62, 31.62$
- Closest point on line: $\left(-\frac{15}{26}, \frac{3}{26}\right)$