4.1.310 AP calculus Exam Area under to functions

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Discussion Overview

The discussion revolves around solving a problem from an AP Calculus exam related to finding the area between two functions, specifically the natural logarithm function and a linear function. Participants explore methods to find the intersection points and evaluate integrals to determine the area under the curves.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in isolating x from the equation $$\ln x = 5-x$$ and questions how to proceed.
  • Another participant notes that the problem is calculator active and provides a transformation of the functions to facilitate integration.
  • There is a suggestion that knowing the x-coordinate of the intersection may not be necessary for solving part (a) of the problem.
  • However, a later reply asserts that both x and y coordinates of the intersection point are needed for different parts of the problem, emphasizing the use of integrals with respect to y for part (a) and x for part (b).
  • Some participants indicate a preference for focusing on part (c) of the problem, which is described as a free response question.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of finding the intersection coordinates for various parts of the problem, indicating a lack of consensus on the approach to take.

Contextual Notes

There are unresolved aspects regarding the exact values of the intersection points and the specific integrals needed for each part of the problem, as well as the dependence on the definitions of the functions involved.

karush
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ok I got stuck real soon...

.a find where the functions meet $$\ln x = 5-x$$
e both sides
$$x=e^{5-x}$$ok how do you isolate x?

W|A returned $x \approx 3.69344135896065...$
but not sure how they got itb.?
c.?
 

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FYI, this is a calculator active problem ...

$y = \ln{x} \implies x = e^y$

$y = 5-x \implies x = 5-y$

$$R = \int_0^{1.3065586} (5-y) - e^y \, dy = 2.986$$
 

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so then we don't need to know x of the intersection
 
karush said:
so then we don't need to know x of the intersection

yes, you need both x and y coordinates of the intersection point ...

(a) can be done w/r to x or y ... I went w/r to y because it only requires a single integral expression

(b) requires x ... two integrals

(c) requires y
 
ill go with c
 
karush said:
ill go with c

?

(c) is a free response question, not a choice
 

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