Square root of 4.1- do you have to use calculus?

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Discussion Overview

The discussion revolves around the question of whether calculating the square root of 4.1 requires calculus or if it can be done using simpler arithmetic methods. Participants explore various methods, including Newton's method and other approximation techniques, while also considering how calculators compute square roots.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether a simple arithmetic method exists for calculating the square root of 4.1 or if calculus is necessary, specifically mentioning the "tangent line approximation formula."
  • Another participant suggests that the "tangent line approximation method" refers to Newton's method and proposes an iterative sequence that converges to the square root.
  • There is a discussion about the limitations of both Newton's method and the proposed arithmetic method, noting that neither provides exact results to all significant figures.
  • A participant expresses curiosity about how calculators achieve their results, leading to the clarification that calculators use approximation algorithms and do not provide exact results due to their finite digit display.
  • One participant points out that the square root of 4.1 can be expressed as a ratio of square roots, highlighting that both components are irrational and cannot be represented as finite decimal expansions.
  • Another participant notes that while calculators display a finite number of digits, those digits represent the correct initial digits of the decimal expansion of the number.

Areas of Agreement / Disagreement

Participants generally agree that calculators do not provide exact results and that approximation methods are used. However, there is no consensus on what constitutes a "simple" arithmetic method for calculating square roots, and the discussion includes multiple viewpoints on the effectiveness of different methods.

Contextual Notes

Participants express uncertainty regarding the definitions of "simple" methods and the precision of results obtained through various techniques. The discussion also highlights the limitations of numerical approximations in achieving exact values.

Femme_physics
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Square root of 4.1-- do you have to use calculus?

In order to solve square root of 4.1, is there a simple arithmetic method or do you have to use calculus and use that "tangent line approximation formula"?

I wonder how do calculators do it... does anybody know?
 
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I'm assuming you by "tangent line approximation method" you mean Newton's method. What exactly is wrong with it?

I suppose if you wanted a more "elementary method", you could the following:
<br /> x_{n+1} = \frac{1}{2} (x_n + \frac{4.1}{x_n} )<br />

That sequence will converge to your square root, and it's an analog of Newton's method.
 


Oh, okay, I see the next topic in my book is Newton's method. Guess I should've read that first :shy:
 


Okay, I read Newton's method. Both methods don't give the exact results (to all sig fig). Do calculators give the exact result? I wonder.
 


Question: what book are you reading?
 


Calculus textbook, of course! It's produced by the OpenU of my country (IL)
 


Dory said:
Okay, I read Newton's method. Both methods don't give the exact results (to all sig fig). Do calculators give the exact result? I wonder.

No, calculators don't give an exact result, in general. How could they, since they only display a finite number of digits? They use an approximation algorithm like the one described above.
 


Dory said:
Okay, I read Newton's method. Both methods don't give the exact results (to all sig fig). Do calculators give the exact result? I wonder.
\sqrt{4.1}= \frac{\sqrt{41}}{\sqrt{10}}

Neither 41 nor 10 is a perfect square so their square roots are irrational. Further, they have no common factors so the ratio of \sqrt{41} to \sqrt{10} is irrational. It cannot be written as a finite decimal expansion nor as a ratio of integers (fraction). No, calculators do not give an exact result for a problem like that- the exact result cannot be written in any "place value" notation.
 
  • #10


Note, however, that if the calculator displays n digits of the result, those n digits are the correct first n digits of the decimal expansion of the number. The approximative methods allow you to calculate the correct digits up to any precision you desire.
 
  • #11


Thanks Halls, guys. That pretty much clears it up for me :)
 

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