Chapter 6: Problem 13
Evaluate. $$ \int_{0}^{2} \int_{0}^{x}\left(x+y^{2}\right) d y d x $$
Short Answer
Expert verified
The value of the double integral is 4.
Step by step solution
01
Understand the Integral
The given double integral is \( \int_{0}^{2} \int_{0}^{x} (x+y^2) \, dy \, dx \). This means we first integrate with respect to \( y \) while treating \( x \) as a constant, and then integrate the result with respect to \( x \).
02
Inner Integral with Respect to y
Integrate \( x+y^2 \) with respect to \( y \) from \( 0 \) to \( x \).\[\int_{0}^{x} (x + y^2) \, dy = \int_{0}^{x} x \, dy + \int_{0}^{x} y^2 \, dy \] Evaluate each separately:\(\int_{0}^{x} x \, dy = [xy]_0^x = x(x) - x(0) = x^2 \)\(\int_{0}^{x} y^2 \, dy = \left[ \frac{y^3}{3} \right]_0^x = \frac{x^3}{3} - \frac{0^3}{3} = \frac{x^3}{3} \)Combine the results:\( x^2 + \frac{x^3}{3} \) is the result of the inner integration.
03
Outer Integral with Respect to x
Integrate the result from the previous step with respect to \( x \) from \( 0 \) to \( 2 \):\[\int_{0}^{2} \left( x^2 + \frac{x^3}{3} \right) \, dx = \int_{0}^{2} x^2 \, dx + \int_{0}^{2} \frac{x^3}{3} \, dx\]Evaluate each separately:\(\int_{0}^{2} x^2 \, dx = \left[ \frac{x^3}{3} \right]_0^2 = \frac{2^3}{3} - \frac{0^3}{3} = \frac{8}{3} \)\(\int_{0}^{2} \frac{x^3}{3} \, dx = \frac{1}{3}\left[ \frac{x^4}{4} \right]_0^2 = \frac{1}{3} \left( \frac{16}{4} - \frac{0}{4} \right) = \frac{16}{12} = \frac{4}{3} \)Add the results:\( \frac{8}{3} + \frac{4}{3} = \frac{12}{3} = 4 \).
04
Final Step: Solution Conclusion
The final result of the double integral \( \int_{0}^{2} \int_{0}^{x} (x+y^2) \, dy \, dx \) is determined to be 4.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Calculus
Calculus is a branch of mathematics that studies how things change. It's like a super tool that helps us describe and understand motion and growth.
In this context, we're using calculus to evaluate a double integral, which is essentially the same as finding the area or volume under a surface defined by a function.
Calculus helps us break down complex problems into manageable pieces, making it easier to find precise solutions.
In this context, we're using calculus to evaluate a double integral, which is essentially the same as finding the area or volume under a surface defined by a function.
Calculus helps us break down complex problems into manageable pieces, making it easier to find precise solutions.
- Differentiation: This involves finding the rate of change of a function.
- Integration: This is the process of finding the total accumulation, like area under a curve.
Inner Integral
The inner integral is the first step in solving a double integral problem. It's all about focusing on one variable at a time while treating the other variables as constants.
In the equation \( \int_{0}^{x} (x + y^2) \, dy \), we start by integrating with respect to \( y \). This means we treat \( x \) as a fixed number and find the integral of \( x+y^2 \) over the limits from 0 to \( x \).
In the equation \( \int_{0}^{x} (x + y^2) \, dy \), we start by integrating with respect to \( y \). This means we treat \( x \) as a fixed number and find the integral of \( x+y^2 \) over the limits from 0 to \( x \).
- Separate the terms: \( x \) is treated as a constant during the integration with respect to \( y \).
- Integrate every term: Calculate separately for \( x \) and \( y^2 \), then combine the results.
- Apply limits: Substitute in the limits for \( y \), here from 0 to \( x \), to get the expression for just \( x \).
Outer Integral
Once the inner integral is solved, the result is then used as a new function in the outer integral.
For our exercise, after solving the inner integral, we obtain \( x^2 + \frac{x^3}{3} \). This expression needs to be integrated with respect to \( x \), from 0 to 2.
For our exercise, after solving the inner integral, we obtain \( x^2 + \frac{x^3}{3} \). This expression needs to be integrated with respect to \( x \), from 0 to 2.
- Apply integration rules: Use the simple power rule to integrate each term in the expression.
- Evaluate between limits: Substitute these limits into the integral result to find the total accumulation.
- Sum up: Add up the results of each integral to get the final result.