Chapter 6: Problem 50
(a) Find the number a such that the line \(x=a\) bisects the area under the curve \(y=1 / x^{2}, 1 \leqslant x \leqslant 4 .\) (b) Find the number \(b\) such that the line \(y=b\) bisects the area in part (a).
Short Answer
Expert verified
(a) \(a = \frac{8}{5}\), (b) \(b = \frac{1}{16}\).
Step by step solution
01
Understanding the Problem
We are given the curve \(y = \frac{1}{x^2}\) and need to find two separate bisecting lines. For part (a), we find \(x = a\) that halts the area under this curve between 1 and 4 into two equal parts. For part (b), we find \(y = b\) which cuts the area found in part (a) vertically equally.
02
Calculate Total Area under Curve
First, find the integral of \(y = \frac{1}{x^2}\) from \(x = 1\) to \(x = 4\). This gives the total area under the curve. The integral is \(\int_{1}^{4} \frac{1}{x^2} \, dx\). This evaluates to \(-\frac{1}{x}\) from 1 to 4, which results in \(-\frac{1}{4} + 1 = \frac{3}{4}\).
03
Write Equation for Bisecting Line x=a
We need to find \(a\) such that the integral from 1 to \(a\) equals half the total area. The equation becomes \(\int_{1}^{a} \frac{1}{x^2} \, dx = \frac{3}{8}\).
04
Solving the Integral Equation
The antiderivative of \(\frac{1}{x^2}\) is \(-\frac{1}{x}\). We find \(-\frac{1}{a} + 1 = \frac{3}{8}\). Simplifying gives \(-\frac{1}{a} = \frac{3}{8} - 1\), which results in \(-\frac{1}{a} = -\frac{5}{8}\). Solving for \(a\) gives \(a = \frac{8}{5}\).
05
Check Area for x=a
Verify \(a = \frac{8}{5}\) by calculating area on each side: \(\int_{1}^{\frac{8}{5}} \frac{1}{x^2} \, dx = \frac{3}{8}\) and \(\int_{\frac{8}{5}}^{4} \frac{1}{x^2} \, dx = \frac{3}{8}\) confirm bisected area. Both integrals confirm correctness.
06
Find the Bisecting Line y=b
Now, we need \(y = b\) to bisect this area horizontally. This involves finding the \(b\) that makes the total area under \(y = b\) equals to half of \(\frac{3}{8}\). We set \(b \times (4 - 1) = \frac{3}{16}\) because width equals 3.
07
Solving for y=b
Solve \(3b = \frac{3}{16}\); hence, \(b = \frac{1}{16}\). This provides the horizontal bisection of the region between the curve and the x-axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Area Under Curve
Understanding the concept of the "area under a curve" is crucial when dealing with calculus problems like the one presented. The area under the curve represents the integral of a function, which is essentially the accumulation of values, or the entire "mass" of the function plotted against the x-axis over a specific interval.
For the given exercise, we are dealing with the curve described by the function \( y = \frac{1}{x^2} \). To find the area under this curve from \( x = 1 \) to \( x = 4 \), we calculate the definite integral within these bounds.
For the given exercise, we are dealing with the curve described by the function \( y = \frac{1}{x^2} \). To find the area under this curve from \( x = 1 \) to \( x = 4 \), we calculate the definite integral within these bounds.
- This involves calculating \( \int_{1}^{4} \frac{1}{x^2} \, dx \), resulting in an area of \( \frac{3}{4} \).
- Conceptually, splitting this area evenly means finding the point \( x = a \) such that the area from 1 to \( a \) equals half of \( \frac{3}{4} \).
Integration
Integration is a fundamental concept in calculus, playing a central role in analyzing areas under curves. When integrating a function, you're essentially summing up infinitely small quantities to determine the total accumulation over an interval.
In the exercise,
In the exercise,
- We integrate \( \frac{1}{x^2} \) over specified bounds to find total and partial areas.
- The integral of \( \frac{1}{x^2} \), in this case, evaluated from 1 to 4 gives \( -\frac{1}{x} \),converted from the form of a power rule where \( y = x^{-2} \).
- The solution helps identify the splitting point \( x = a \), where the integral from 1 to \( a \) provides \( \frac{3}{8} \).
Definite Integral
Definite integrals allow us to compute the exact area under a curve between two specific points on the x-axis. Unlike indefinite integrals, which produce a general antiderivative, definite integrals give a specific numerical value representing area.
For instance,
For instance,
- The problem asks to find how a line \( x = a \) bisects the area, requiring evaluation of \( \int_{1}^{a} \frac{1}{x^2} \, dx \).
- Solving the definite integral yields a step-by-step path to not only calculating areas but finding precise numerical solutions, such as \( a = \frac{8}{5} \), where the area is bisected.
- Other examples include calculating further, \( y = b \), where the problem similarly bisects half the previously bisected area.