Chapter 21: Problem 53
The shortest distance between the point \(\left(\frac{3}{2}, 0\right)\) and the curve \(y=\sqrt{x},(x>0)\), is: \(\quad\) [Jan. 10, 2019 (I)] (a) \(\frac{\sqrt{5}}{2}\) (b) \(\frac{\sqrt{3}}{2}\) (c) \(\frac{3}{2}\) (d) \(\frac{5}{4}\)
Short Answer
Expert verified
The shortest distance is \(\frac{\sqrt{5}}{2}\), (a).
Step by step solution
01
Identify the Objective
We need to find the shortest distance from the point \( \left(\frac{3}{2}, 0\right) \) to the curve \( y = \sqrt{x} \), where \( x > 0 \). This involves minimizing the distance from the point to the curve.
02
Express the Distance Formula
The distance \( D \) between a point \( (x_1, y_1) \) and another point \( (x, y) \) is given by the formula \( D = \sqrt{(x - x_1)^2 + (y - y_1)^2} \). Substituting \( x_1 = \frac{3}{2}, y_1 = 0, y = \sqrt{x} \), the distance from point \( \left(\frac{3}{2}, 0\right) \) to a point \( (x, \sqrt{x}) \) on the curve is \( D(x) = \sqrt{(x - \frac{3}{2})^2 + x} \).
03
Set Up the Function for Optimization
We want to minimize \( D(x) = \sqrt{(x - \frac{3}{2})^2 + x} \). To simplify, we can minimize the square of the distance, \( D^2(x) = (x - \frac{3}{2})^2 + x \) because the square and the square root functions are both strictly increasing.
04
Differentiate the Distance Function
Let \( f(x) = (x - \frac{3}{2})^2 + x \). Differentiate with respect to \( x \): \[ f'(x) = 2(x - \frac{3}{2}) + 1 = 2x - 3 + 1 = 2x - 2 \].
05
Find the Critical Points
Set the derivative equal to zero to find the critical points: \[ 2x - 2 = 0 \] \[ 2x = 2 \] \[ x = 1 \].
06
Evaluate the Distance at the Critical Point
Evaluate \( D(x) \) at \( x = 1 \): The point on the curve is \( (1, \sqrt{1}) = (1, 1) \). The distance is: \[ D = \sqrt{(1 - \frac{3}{2})^2 + (1 - 0)^2} = \sqrt{(-\frac{1}{2})^2 + 1} = \sqrt{\frac{1}{4} + 1} = \sqrt{\frac{5}{4}} = \frac{\sqrt{5}}{2} \].
07
Conclusion
The shortest distance from the point \( \left(\frac{3}{2}, 0\right) \) to the curve \( y = \sqrt{x} \) is \( \frac{\sqrt{5}}{2} \), which corresponds to option (a).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Distance Formula
The Distance Formula is a vital concept in geometry and algebra, helping us measure the straight-line distance between two points in a plane. Imagine you have two points, say \((x_1, y_1)\) and \((x_2, y_2)\). The formula for calculating the distance between these points is given by: \[D = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}\]
In our exercise, the Distance Formula helps us calculate how far \(\left(\frac{3}{2}, 0\right)\) is from any point \(x, \sqrt{x}\)\ on the curve \(y = \sqrt{x}\). This foundational step allows us to proceed towards finding the shortest possible distance by using optimization techniques.
- "D" represents the distance between the two points.
- The expression inside the square root is the sum of the squares of the differences in the x-coordinates and y-coordinates.
In our exercise, the Distance Formula helps us calculate how far \(\left(\frac{3}{2}, 0\right)\) is from any point \(x, \sqrt{x}\)\ on the curve \(y = \sqrt{x}\). This foundational step allows us to proceed towards finding the shortest possible distance by using optimization techniques.
Optimization
Optimization is all about finding the best solution to a problem. In the context of this exercise, we are searching for the shortest distance between a specific point and a curve. When you want to optimize a function, it's often useful to consider minimizing or maximizing it. With distance problems, minimizing the squared distance instead of the actual distance is usually more convenient mathematically.
- We work with \(f(x) = (x - \frac{3}{2})^2 + x\), which is the function for the squared distance.
- We find a point where the slope of \(f(x)\) is zero, meaning we've found a local minimum or maximum.
Curve Analysis
Curve Analysis involves understanding how a curve behaves and is applied here to find the least distance from a point to a curve. In this problem, analyzing \(y = \sqrt{x}\) is crucial.The curve \(y = \sqrt{x}\) is part of the family of functions known as root functions. This particular curve starts at \(x = 0\) and gently rises as \(x\) increases, with a characteristic curve.
- The point \((1, 1)\) is found during evaluation at the critical point \(x = 1\). It lies on our curve \(y = \sqrt{x}\).
- This corresponds to the shortest path from \(\left(\frac{3}{2}, 0\right)\) to the curve.