Math Problem Statement

the region in the xy-plane defined by the inequalities x − 3y2 ≥ 0, 2 − x − 5|y| ≥ 0 find its area.

Solution

We are given two inequalities that define a region in the xyxy-plane:

  1. x3y20x - 3y^2 \geq 0
  2. 2x5y02 - x - 5|y| \geq 0

Step 1: Analyze the First Inequality

The inequality x3y20x - 3y^2 \geq 0 can be rewritten as: x3y2x \geq 3y^2 This represents a region to the right of the parabola x=3y2x = 3y^2.

Step 2: Analyze the Second Inequality

The inequality 2x5y02 - x - 5|y| \geq 0 can be rewritten as: x25yx \leq 2 - 5|y| This describes a region to the left of the line x=25yx = 2 - 5|y|, where y|y| represents the absolute value of yy, so we need to treat the cases for y0y \geq 0 and y<0y < 0.

Step 3: Find the Boundary Points

To find the points where these curves intersect, we set the expressions for xx equal to each other:

3y2=25y3y^2 = 2 - 5|y|

Case 1: y0y \geq 0

For y0y \geq 0, the absolute value simplifies to y=y|y| = y, so the equation becomes: 3y2=25y3y^2 = 2 - 5y Rearranging this: 3y2+5y2=03y^2 + 5y - 2 = 0 Solving this quadratic equation using the quadratic formula: y=5±524(3)(2)2(3)=5±25+246=5±496=5±76y = \frac{-5 \pm \sqrt{5^2 - 4(3)(-2)}}{2(3)} = \frac{-5 \pm \sqrt{25 + 24}}{6} = \frac{-5 \pm \sqrt{49}}{6} = \frac{-5 \pm 7}{6} This gives two solutions: y=5+76=26=13,y=576=126=2y = \frac{-5 + 7}{6} = \frac{2}{6} = \frac{1}{3}, \quad y = \frac{-5 - 7}{6} = \frac{-12}{6} = -2

Case 2: y<0y < 0

For y<0y < 0, y=y|y| = -y, so the equation becomes: 3y2=2+5y3y^2 = 2 + 5y Rearranging this: 3y25y2=03y^2 - 5y - 2 = 0 Solving this quadratic equation: y=5±(5)24(3)(2)2(3)=5±25+246=5±496=5±76y = \frac{5 \pm \sqrt{(-5)^2 - 4(3)(-2)}}{2(3)} = \frac{5 \pm \sqrt{25 + 24}}{6} = \frac{5 \pm \sqrt{49}}{6} = \frac{5 \pm 7}{6} This gives two solutions: y=5+76=126=2,y=576=26=13y = \frac{5 + 7}{6} = \frac{12}{6} = 2, \quad y = \frac{5 - 7}{6} = \frac{-2}{6} = \frac{-1}{3} However, since this case is for y<0y < 0, only y=13y = -\frac{1}{3} is valid.

Step 4: Set the Limits and Calculate the Area

The region is symmetric about the xx-axis due to the absolute value in the second inequality, so we can calculate the area for y0y \geq 0 and double it.

The limits of integration for y0y \geq 0 are from y=0y = 0 to y=13y = \frac{1}{3}. The area is determined by the difference between the curves: x=25yandx=3y2x = 2 - 5y \quad \text{and} \quad x = 3y^2 Thus, the area for y0y \geq 0 is: Area=01/3((25y)3y2)dy\text{Area} = \int_0^{1/3} \left( (2 - 5y) - 3y^2 \right) \, dy

Now, let's compute this integral.The total area of the region defined by the inequalities x3y20x - 3y^2 \geq 0 and 2x5y02 - x - 5|y| \geq 0 is approximately 0.7040.704 square units.

Would you like more details, or do you have any questions?

Here are 5 related questions to consider:

  1. How does symmetry simplify the calculation of areas in regions like this?
  2. What is the geometric interpretation of the curves involved in the inequalities?
  3. How can the quadratic formula help in solving intersection points between curves?
  4. How would the result change if the coefficients in the inequalities were different?
  5. What other methods can be used to find areas under curves besides integration?

Tip: Symmetry is a powerful tool in integration, often allowing you to compute only half the area and then multiply by two to get the total area.

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Math Problem Analysis

Mathematical Concepts

Inequalities
Quadratic Equations
Absolute Value
Integration
Area under Curves

Formulas

x - 3y^2 ≥ 0 (Parabolic inequality)
2 - x - 5|y| ≥ 0 (Linear inequality with absolute value)
Quadratic formula: x = (-b ± √(b^2 - 4ac)) / 2a
Area formula: ∫[a,b] (f(y) - g(y)) dy

Theorems

Symmetry of regions about the x-axis
Quadratic formula for solving quadratic equations
Integration of curves to find the area between them

Suitable Grade Level

Grades 11-12 (Pre-Calculus/Calculus)