How to Find the Point of Intersection Between ln x and 5-x?

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Discussion Overview

The discussion revolves around finding the point of intersection between the functions $\ln x$ and $5-x$. Participants explore various mathematical approaches to determine this intersection, including integrals and volume calculations. The scope includes mathematical reasoning and problem-solving techniques.

Discussion Character

  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant suggests that the point of intersection can be calculated as $x=3.69344$, but hints at the possibility of a simpler approach.
  • Another participant proposes using integrals to express the area between the curves, defining $R$ in terms of the intersection point $a$.
  • A different approach is introduced involving the volume calculated by integrating $(\ln{x})^2$ and $(5-x)^2$ over specified intervals.
  • Further discussion includes a modification of the variable in the integral setup, suggesting a relationship between the area $A$ and the intersection point $k$.

Areas of Agreement / Disagreement

Participants present multiple competing views on how to approach the problem, and the discussion remains unresolved with no consensus on a single method or solution.

Contextual Notes

Some assumptions regarding the limits of integration and the definitions of variables are not explicitly stated, which may affect the interpretation of the proposed methods.

karush
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Ok this might take a while...
but first find point of intersection $\ln x=5-x$
which calculates to $x=3.69344$ which maybe there is more simpler approach
 
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this is a calculator active problem ...

$\displaystyle R = \int_1^a \ln{x} \, dx + \int_a^5 5-x \, dx$
where $a$ is the x-value of the intersection.

or ...
$\displaystyle R = \int_0^b (5-y) - e^y \, dy$
where $b$ is the y-value of the intersection.

can you set up the volume by similar cross-section integral ?
 
$\displaystyle V = \int_1^a (\ln{x})^2\, dx + \int_a^5 (5-x)^2 \, dx$
 
ok ... continue with part (c)
 
skeeter said:
ok ... continue with part (c)
if we chanhge b to k
$\displaystyle \int_0^k (5-y) - e^y \, dy = \dfrac{1}{2} A$
then solve for k y was derived previous
anyway...
 

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