/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 14 Suppose that \(\int_{6}^{8}(3 f(... [FREE SOLUTION] | 91Ó°ÊÓ

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Suppose that \(\int_{6}^{8}(3 f(x)-x) d x=6\) and \(\int_{8}^{6}(2 x+4 g(x)) d x=-8 .\) Evaluate \(\int_{8}^{6}(f(x)-5 g(x)) d x\).

Short Answer

Expert verified
The value of \( \int_{8}^{6}(f(x)-5 g(x)) d x \) is 14.

Step by step solution

01

Understanding the Problem

We are given the integrals \( \int_{6}^{8}(3 f(x)-x) d x=6 \) and \( \int_{8}^{6}(2 x+4 g(x)) d x=-8 \). We need to evaluate the integral \( \int_{8}^{6}(f(x)-5 g(x)) d x \). The limits of the integral need careful attention since they are not in their standard increasing order.
02

Changing the Integration Limits

Notice that the second integral \( \int_{8}^{6} \) is not in standard form (lower limit to upper limit), but it equals -8. Reversing the limits changes the sign, so \( \int_{6}^{8}(2 x+4 g(x)) d x = 8 \).
03

Expressing the Required Integral

We need to express \( \int_{8}^{6}(f(x)-5 g(x)) d x \) in terms of the given integrals. This involves rearranging and possibly combining the given expressions using algebra.
04

Utilizing Given Information

Solve the given integrals: We know \( \int_{6}^{8}(3 f(x)-x) d x=6 \) implies \( 3 \int_{6}^{8}f(x) dx - \int_{6}^{8}x dx = 6 \). Separately, \( \int_{6}^{8}(2x+4g(x)) d x = 8 \) implies \( 2 \int_{6}^{8}x dx + 4 \int_{6}^{8}g(x) dx = 8 \).
05

Relating Integrals

From the above equations, find individual integrals: \( 3 \int_{6}^{8}f(x) dx - \int_{6}^{8}x dx = 6 \). Let \( I_1 = \int_{6}^{8}f(x) dx \) and \( I_2 = \int_{6}^{8}g(x) dx \). The second equation gives \( 2\int_{6}^{8}x dx + 4I_2 = 8 \).
06

Subtracting the Reversed Limits

The given problem requires \( \int_{6}^{8} (f(x) - 5g(x)) dx = -\int_{8}^{6} (f(x) - 5g(x)) dx \). Use the expression: \( I_1 - 5I_2 = \) subtract the combined contributions.
07

Calculating the Final Result

Substitute the equations in terms of \( I_1 \) and \( I_2 \), and perform algebra to extract and calculate \( \int_{6}^{8} (f(x) - 5g(x)) dx \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Reverse Limits
When dealing with definite integrals, the order of the limits of integration can affect the outcome. Typically, the limits are arranged from lower to upper, i.e., the lower limit first followed by the upper limit.

However, if the limits are reversed, such as in \ \ \( \int_\text{upper}\text{to}\text{lower} \), this results in the integral being the negative of what it would be with the limits in the usual order. For example, reversing the limits of \( \int_{8}^{6}(2x+4g(x)) dx \) turns it into \( \int_{6}^{8}(2x+4g(x)) dx \) and changes the integral's value from \(-8\) to \(8\).
  • This property is vital because it allows manipulation of integrals to standardize their forms and easily relate them to each other.
  • Remember, if an integral with reversed limits is given, convert it by changing the sign to simplify problem-solving.
Reversing the limits is a powerful tool in calculus as it helps in calculations where backward integrals are provided or needed.
Algebraic Manipulation
Algebraic manipulation is often required to rearrange and combine the expressions in integrals for straightforward evaluation. Let's look at how it's applied in definite integration problems. For example, consider the integral equation \( 3\int_{6}^{8}f(x)dx - \int_{6}^{8}xdx = 6 \).

We use algebraic manipulation to isolate the desired integral, \( \int_{6}^{8}f(x)dx \), by expressing it in terms of known integrals.
  • Algebraic manipulation involves operations such as addition, subtraction, multiplication, or division applied to rearrange terms and isolate variables.
  • In problems involving multiple integrals, add or subtract other known integrals to derive new expressions and solve for unknown integrals.
This process is essential to handle complex integral expressions and make sense of given integral equations effectively.
Integral Properties
Understanding integral properties is key to solving definite integration problems efficiently. One crucial property is linearity, which allows you to simplify and manipulate integrals easily. Linearity indicates that the integral of a sum is the sum of integrals, and the integral of a constant multiplied by a function is the constant multiplied by the integral of that function.

Let's apply this: given \( \int_{6}^{8}(3f(x) - x) dx = 6 \), the linearity property lets us express it as \( 3\int_{6}^{8}f(x) dx - \int_{6}^{8}x dx = 6 \).
  • Linearity facilitates separating integral components to solve for specific parts, simplifying complex integral expressions.
  • Moreover, when reverse limit integrals or combined integrals are involved, the linearity property can be used to break down or reconstruct the given equations.
Make sure to understand these properties well, as they are immensely helpful when dealing with expressions that must be rearranged or simplified as seen in the exercise.

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Most popular questions from this chapter

Express the area of the given region as a sum of integrals of the form \(\int_{a}^{b} f(x) d x\). The region enclosed by \(y=|x|\) and \(y=2-x^{2}\)

A sum of integrals of the form \(\int_{a}^{b} f(x) d x\) is given. Express the sum as a single integral of form \(\int_{c}^{d} g(y) d y\). $$ \int_{0}^{2} \sqrt{x} d x=\int_{2}^{4} \sqrt{4-x} d x $$

Find the area of the region that is bounded by the graphs of \(y=f(x)\) and \(y=g(x)\) for \(x\) between the abscissas of the two points of intersection. $$ f(x)=x^{2}+5 \quad g(x)=2 x^{2}+1 $$

The integral \(\int_{a}^{b}\left(f_{1}(x)-f_{2}(x)\right) d x\) represents the area of a region in the \(x y\) -plane that is bounded by the graphs of \(f_{1}\) and \(f_{2}\). Express the area of the region as an integral of the form \(\int_{c}^{d}\left(g_{1}(y)-g_{2}(y)\right) d y .\) For example, the integral \(\int_{0}^{1}\left(x-x^{2}\right) d x\) represents the area of the shaded region in Figure \(11 .\) This area can also be represented as \(\int_{0}^{1}(\sqrt{y}-y) d y.\) $$ \int_{0}^{4}(\sqrt{x}-x / 2) d x $$

In a particular regional climate, the temperature varies between \(-22^{\circ} \mathrm{C}\) and \(40^{\circ} \mathrm{C}\), averaging \(\mu=11^{\circ} \mathrm{C}\). The number of days \(F(T)\) in the year on which the temperature remains below \(T\) degrees centigrade is given (approximately) by $$F(T)=\int_{-22}^{T} f(x) d x \quad(-22 \leq T \leq 40)$$ where $$f(x)=12.72 \exp \left(-\frac{(x-11)^{2}}{266.4}\right) $$ Notice that \(F(T)\) is the sort of area integral that we studied in Section 5.4 . a. Use Simpson's Rule with \(N=20\) to approximate \(F(40) .\) What should the exact value of \(F(40)\) be? b. Heat alerts are issued when the daily high temperature is \(36^{\circ} \mathrm{C}\) or more. On about how many days a year are heat alerts issued? c. Suppose that global warming raises the average temperature by \(1^{\circ} \mathrm{C}\), shifting the graph of \(f\) by 1 unit to the right. The new model may be obtained by simply replacing \(\mu\) with 12 and using [-21,41] as the domain (see Figure 13). What is the percentage increase in heat alerts that will result from this \(1^{\circ} \mathrm{C}\) shift in temperature?

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