Math Problem Statement

Đổi thứ tự lấy tích phân sau: I = ∫₀^(1/2) ∫₁^(1+√(2y-y²)) f(x, y) dx dy + ∫_(1/2)^1 ∫_(2y)^(1+√(2y-y²)) f(x, y) dx dy.

Solution

This is a calculus problem involving changing the order of integration in a double integral. Let's carefully analyze the given integral and steps for changing the order.

The integral is:

I=01211+2yy2f(x,y)dxdy+1212y1+2yy2f(x,y)dxdy.I = \int_0^{\frac{1}{2}} \int_1^{1 + \sqrt{2y - y^2}} f(x, y) \, dx \, dy + \int_{\frac{1}{2}}^1 \int_{2y}^{1 + \sqrt{2y - y^2}} f(x, y) \, dx \, dy.

Step 1: Understand the region of integration

The region is defined by the bounds:

  1. For 0y120 \leq y \leq \frac{1}{2}, xx varies from x=1x = 1 to x=1+2yy2x = 1 + \sqrt{2y - y^2}.
  2. For 12y1\frac{1}{2} \leq y \leq 1, xx varies from x=2yx = 2y to x=1+2yy2x = 1 + \sqrt{2y - y^2}.

These describe two regions in the xx-yy plane. Combining these, the overall region in the xx-yy plane needs to be analyzed for converting the order of integration.

Step 2: Analyze boundaries

The boundaries are derived from the equations x=1x = 1, x=1+2yy2x = 1 + \sqrt{2y - y^2}, and x=2yx = 2y, as well as the range for yy: 0y10 \leq y \leq 1.

  • From x=1+2yy2x = 1 + \sqrt{2y - y^2}, rewrite as: 2yy2=x1    2yy2=(x1)2.\sqrt{2y - y^2} = x - 1 \implies 2y - y^2 = (x - 1)^2. Expanding and rearranging gives: y22y+(x1)2=0,y^2 - 2y + (x - 1)^2 = 0, which is a quadratic equation in yy. This represents part of a parabolic boundary.

  • The line x=2yx = 2y is another boundary in the region.

Step 3: New bounds for xx and yy

We need to rewrite the region with the roles of xx and yy swapped. Observing the graph, the new bounds are:

  1. xx ranges from 11 to 22.
  2. For a fixed xx, yy ranges between the lines and curves that bound the region.

The new integral becomes: I=12g1(x)g2(x)f(x,y)dydx,I = \int_1^2 \int_{g_1(x)}^{g_2(x)} f(x, y) \, dy \, dx, where g1(x)g_1(x) and g2(x)g_2(x) represent the lower and upper bounds for yy as a function of xx.

  • For x[1,32]x \in [1, \frac{3}{2}], yy varies from y=0y = 0 (bottom edge) to y=x12y = \frac{x-1}{2} (from x=2yx = 2y).
  • For x[32,2]x \in [\frac{3}{2}, 2], yy varies from y=0y = 0 to y=122x+x2y = 1 - \sqrt{2 - 2x + x^2} (from the parabola).

Final Answer

The changed order of integration is: I=1320x12f(x,y)dydx+3220122x+x2f(x,y)dydx.I = \int_1^{\frac{3}{2}} \int_0^{\frac{x-1}{2}} f(x, y) \, dy \, dx + \int_{\frac{3}{2}}^2 \int_0^{1 - \sqrt{2 - 2x + x^2}} f(x, y) \, dy \, dx.

Would you like a detailed explanation of any step? Let me know!


Related Questions:

  1. How do you derive the equations of boundaries in a double integral problem?
  2. What are the general principles for changing the order of integration in double integrals?
  3. How can the quadratic equation y22y+(x1)2=0y^2 - 2y + (x-1)^2 = 0 be solved explicitly for yy?
  4. How does the geometric interpretation of integration regions simplify problems like this?
  5. What methods can verify if the rewritten integral is equivalent to the original?

Tip:

When swapping the order of integration, always sketch the region to visualize the boundaries. This prevents errors in setting the new bounds!

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Double Integration
Changing the Order of Integration
Integral Bounds

Formulas

Double integral formula ∫∫ f(x, y) dx dy
Boundary equations: x = 1, x = 1 + √(2y - y²), x = 2y

Theorems

Fubini's Theorem for double integrals

Suitable Grade Level

Undergraduate (Calculus Level)