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Ch. 5 - Integrals
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 5, Problem 5.PE.27

Find the area of the “triangular” region bounded on the left by x + y = 2, on the right by y = x², and above by y = 2.

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First, identify the region bounded by the three curves: the line \( x + y = 2 \), the parabola \( y = x^2 \), and the horizontal line \( y = 2 \). Sketching these curves can help visualize the triangular region.
Rewrite the line equation \( x + y = 2 \) in terms of \( y \) to get \( y = 2 - x \). This will help in setting up the integral.
Determine the points of intersection between the curves to find the limits of integration. Specifically, find where \( y = 2 - x \) intersects \( y = x^2 \), and where these curves intersect \( y = 2 \).
Decide whether to integrate with respect to \( x \) or \( y \). Since the region is bounded vertically by \( y = 2 \) and horizontally by curves expressed as functions of \( x \), integrating with respect to \( y \) might be simpler.
Set up the integral for the area by expressing the horizontal distance between the left and right boundaries as a function of \( y \). For each \( y \) between the lower and upper bounds, find the corresponding \( x \)-values on the line and parabola, then integrate the difference \( x_{right} - x_{left} \) with respect to \( y \) over the appropriate interval.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Finding Points of Intersection

To determine the boundaries of the region, it is essential to find where the given curves intersect. This involves solving equations simultaneously, such as setting y = 2 equal to the other curves or equating x + y = 2 and y = x² to find intersection points that define the limits of integration.
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Setting Up Definite Integrals for Area

The area between curves can be found by integrating the difference of the functions over the interval defined by their intersection points. Identifying which curve is on top or right and which is on bottom or left is crucial to correctly set up the integral representing the area.
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Definition of the Definite Integral

Understanding Region Boundaries in the Plane

Interpreting the problem requires visualizing or sketching the region bounded by the given lines and curves. Recognizing that the region is enclosed by a line, a parabola, and a horizontal line helps in deciding the order of integration and the limits, ensuring the correct calculation of the area.
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Area of Polar Regions