Find Value of Squareroot of 3: Using the Graph & Quadratic Equation

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Discussion Overview

The discussion revolves around determining the value of $\sqrt{3}$ using a graph of the quadratic equation $x^2 - 2x - 3$ and a straight line. Participants explore methods of finding this value through graphical intersection and algebraic manipulation.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests using a straight line in the form of $y = -2x$ to find $\sqrt{3}$ through graphical methods.
  • Another participant questions the relevance of the line $y = -2x$ in determining $\sqrt{3}$, indicating confusion about its application.
  • There is a discussion about the intersection points of the parabola and the line, with one participant noting they intersect at approximately -1.7 and 1.7.
  • A participant proposes a method involving the intersection of the quadratic and a line in the form $y = ax + b$, leading to a derived equation that suggests $a = -2$ and $b = 0$.
  • Another participant emphasizes the importance of experimentation in mathematics, suggesting substituting $\sqrt{3}$ into the quadratic to observe the results.
  • There is a reiteration of the substitution method, with a participant showing the steps taken and questioning what might have gone wrong in their calculations.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness and relevance of the chosen line for determining $\sqrt{3}$. There is no consensus on the best method to approach the problem, and various techniques are proposed without resolution.

Contextual Notes

Participants rely on different assumptions regarding the intersection of the quadratic and linear functions, and the implications of their algebraic manipulations remain unresolved.

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There is a graph in the form of $x^2-2x-3$ determine the value of $\sqrt{3}$ to the nearest decimal place by drawing an a suitable straight line

What must be that straight line ? Usually these kind of problems are solved using the quadratic equation

Many thanks :)
 
Last edited:
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y = -2x
 
Here is the desmos graph including both the parabola and the line

[graph]z2xkzb3xja[/graph]

Looking at the line $y=-2x$ I cannot exactly see what has it got to do with determining $\sqrt{3}$ to the nearest whole number

Many Thanks :)
 
Where do the parabola and line intersect?
 
MarkFL said:
Where do the parabola and line intersect?

Wow (Clapping) they intersect at -1.7 and 1.7.

What was the method used to determine the line?

Many Thanks (Smile)
 
I can't speak for greg1313 and MarkFL but what I would do is note that, if we take equation y= ax+ b, that line and the given quadratic will intersect where [math]x^2- 2x- 3= ax+ b[/math] so that [math]x^2- (2+ a)x- (3+ b)= 0[/math]. If \sqrt{3} is a root then, in order that the coefficients be integers, -\sqrt{3} must also be so that we must have (\sqrt{3})^3- (2+ b)\sqrt{3}- (3+ b)= 3- (2+ a)\sqrt{3}- 3- b= -(2+a)\sqrt{3}- b= 0 and (-\sqrt{3})^2- (2+ b)(-\sqrt{3})- 3- b= 3+ (2+ b)\sqrt{3}- 3- b= (2+a)\sqrt{3}- b= 0. Adding those two equations, the "a" terms cancel giving -b= 0 so b= 0. Then we have -(2+ a)\sqrt{3}= 0 so that 2+ a= 0 and a= -2.
 
Mathematics is a science and experimentation is a valuable tool. The first thing I did was to substitute $\sqrt3$ for $x$ in the given quadratic and observe the results. Get your hands dirty!
 
greg1313 said:
Mathematics is a science and experimentation is a valuable tool. The first thing I did was to substitute $\sqrt3$ for $x$ in the given quadratic and observe the results. Get your hands dirty!

Yes agreed :) By substitution I guess what was implied was replacing all x terms by $\sqrt{3}$

$x^2-2x-3$

$\sqrt{3}^2-2\sqrt{3}-3$

$3-2\sqrt{3}-3$

$-2\sqrt{3}=0=y$

And what possibly went wrong?

Many thanks :)
 
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