Chapter 14: Problem 24
Evaluate the following integrals as they are written. $$\int_{0}^{\ln 2} \int_{e^{x}}^{2} d y d x$$
Short Answer
Expert verified
Question: Evaluate the double integral given by $$\int_{0}^{\ln2}\int_{e^{x}}^{2} dy dx$$
Answer: The value of the double integral is $$2\ln 2 - 3$$.
Step by step solution
01
Integrate with respect to the inner variable, y
Since there is no function inside the integral, we can just integrate 1 with respect to y. The integral of 1 with respect to y is y:
$$\int \int 1 dy dx = \int (y) dx$$
Now we need to find the integral between the given limits for y:
$$\int_{0}^{\ln 2} (2 - e^{x}) d x$$
02
Integrate with respect to the outer variable, x
Now, we find the integral of the function (2 - e^x) with respect to x:
$$\int (2 - e^{x}) d x = 2x - e^{x} + C$$
03
Find the definite integral for the given limits
Now, we need to find the value of the integral between the limits 0 and ln(2) for x:
$$\int_{0}^{\ln 2} (2 - e^{x}) d x = [2x - e^{x}]_{0}^{\ln 2}$$
Now plug in the upper limit, ln(2), and subtract the result when we plug in the lower limit, 0:
$$\left(2(\ln 2) - e^{\ln 2}\right) - \left(2(0) - e^{0}\right) = 2\ln 2 - 2 - 1$$
04
Simplify the final answer
Finally, let's simplify the expression:
$$2\ln 2 - 2 - 1 = 2\ln 2 - 3$$
So, the final answer is:
$$\int_{0}^{\ln2}\int_{e^{x}}^{2} dy dx = 2\ln 2 - 3$$
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Integral Calculus
Integral calculus is a branch of calculus concerned with the theory of integration and its applications. It revolves around the idea of finding the area under a curve. This area represents the integral of a function over a given interval.
In a double integral, like the one in our exercise, we handle functions of two variables. The notation \(\int_{a}^{b}\int_{c}^{d} f(y, x) \, dy \, dx\)is typically used, where we first integrate with respect to \(y\), and then \(x\).
In a double integral, like the one in our exercise, we handle functions of two variables. The notation \(\int_{a}^{b}\int_{c}^{d} f(y, x) \, dy \, dx\)is typically used, where we first integrate with respect to \(y\), and then \(x\).
- This process can be visualized as accumulating small strips in the \(y\)-direction, and stacking them along the \(x\)-direction.
- The double integral essentially helps find volumes under surfaces defined by \(f(y, x)\).
- It's crucial to evaluate these integrals in the correct order unless the limits and function allow for a change of order.
Definite Integrals Explained
Definite integrals are a type of integral with set limits, defining the upper and lower bounds of the area we wish to compute. When you see notations such as \(\int_{a}^{b} f(x) \, dx\), it represents the area from \(a\) to \(b\) under the curve of \(f(x)\).
Compared to indefinite integrals, definite integrals give a numerical value rather than a function. In our exercise:
Compared to indefinite integrals, definite integrals give a numerical value rather than a function. In our exercise:
- The outer integral limits, from \(0\) to \(\ln 2\), represent the bounds for \(x\).
- The inner limits, from \(e^x\) to \(2\), define the bounds for \(y\).
Step-by-Step Evaluation of Integrals
Evaluating an integral involves step-by-step processes to find the accumulated sum described by the integral expression. Let's break down the steps further:
First, when you encounter a double integral:
First, when you encounter a double integral:
- Start by integrating with respect to the innermost variable (here it's \(y\)). This simplification usually turns the inner problem into a basic one-variable integral.
- The forms of upper and lower limits often depend on the other variable, making your \(dy\)integral more like a parameter problem.
- The integral with respect to the outer variable (\(x\) in this example). This usually involves substituting back the results from your first integration.
- Use the antiderivative to plug in the boundary values. Remember to subtract initial values from final values after substitution.