Difficulty finding integral answer to set function

In summary, the question involves finding ∫∫dydx for a set A, which is denoted as the interior and boundary points of a square with opposite vertices at (0,0) and (1,1). A subset C of A is given, and the task is to compute Q(A) using the given set. Although the question is not completely clear, it is determined that for x > 2/3, y < 1. The correct answer is 2/9, which is obtained through the setup ∫^{2/3}_{0}∫^{3x/2}_{x/2}dydx.
  • #1
wown
22
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Note: as i was typing this post, i think i figured out the answer but i want to confirm.
Question:
let A denote the set of points that are interior to, or on the boundary of, a square with opposite verties at the points (0,0) and (1,1). let Q(A) = ∫∫dydx
if C, a subset of A, is the set {(x,y): 0 < x/2 ≤ y ≤ 3x/2 < 1}, compute Q(A)

Solution:
I kept getting 1/2 as the answer, but i think my limits of integration were wrong. is the following correct?

[itex]^{2/3}_{0}[/itex]∫[itex]^{3x/2}_{x/2}[/itex]∫dydx

this setup gives the answer as 2/9... unfortunately i do not have the correct answer which is why i needed to verify.
 
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  • #2
The question is not completely clear. For x > 2/3 is anything included?
This would involve: x/2 < y < 1.
 
  • #3
Unfortunately, i typed the question verbatim and not sure how to respond to you.

note that the 2/3 upper limit on x was defined by me. I figured that y <1 (from y ≤ 3x/2 < 1). so therefor x cannot be more than 2/3, since y must also be less than 3x/2. for x> 2/3, y>1. e.g. when x=1, y=3/2.

does that make sense?
 
  • #4
No. Your condition x/2≤y≤3x/2 for x > 2/3 restricts y to x/2≤y≤1, but does not remove it altogether.
 
  • #5



It's great that you were able to figure out the answer! Your setup looks correct, and it does indeed give the correct answer of 2/9. It's always important to double check our work and verify our solutions, especially when dealing with mathematical concepts like integrals. Keep up the good work!
 

1. Why is it difficult to find an integral answer to a set function?

Integrals are mathematical tools used to calculate the area under a curve or the sum of infinitesimally small values. However, not all functions have an analytical solution for their integral. This means that it is not always possible to find a precise answer for the integral of a set function.

2. What factors contribute to the difficulty in finding an integral answer?

The complexity of the function, the limits of integration, and the type of integral (definite or indefinite) can all contribute to the difficulty in finding an integral answer. Additionally, some functions may not have a closed-form solution and require numerical methods to approximate the integral.

3. What are some common techniques for finding an integral answer to a set function?

Some common techniques for solving integrals include substitution, integration by parts, and trigonometric substitution. These techniques can be used to simplify the function and make it easier to calculate the integral.

4. Can technology be used to find an integral answer?

Yes, technology such as calculators and computer software can be used to find the integral of a set function. These tools use numerical methods to approximate the integral, which can be helpful for functions that do not have a closed-form solution.

5. Are there any alternative methods for calculating the integral of a set function?

Yes, in addition to traditional analytical and numerical methods, there are also other techniques such as contour integration, series expansion, and Laplace transform that can be used to evaluate integrals. However, these methods may not be suitable for all types of functions and may require advanced mathematical knowledge.

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