Finding Continuous Values of $\frac{e^{sinx}}{4 - \sqrt{x^2 - 9}}$

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Discussion Overview

The discussion revolves around determining the continuous values of the function $$\frac{e^{\sin x}}{4 - \sqrt{x^2 - 9}}$$. Participants explore the conditions under which this function remains valid, focusing on the implications of the square root and the denominator.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the function is not valid where $$4 - \sqrt{x^2 - 9} = 0$$, leading to the condition $$x \ne \pm \sqrt{7}$$.
  • Another participant proposes that the condition $$x^2 - 9 \ge 0$$ must be satisfied, resulting in the intervals $$(-\infty, -3] \cup [3, \infty)$$.
  • A similar point is reiterated by another participant, emphasizing the need for $$\sqrt{x^2 - 9} \ne 4$$, leading to the conclusion that $$|x| \ne 5$$.
  • One participant challenges the initial reasoning by pointing out an error in manipulating the inequality $$x^2 - 9 \ne 16$$, suggesting that it should lead to $$x^2 \ne 25$$ instead of $$x^2 \ne 7$$.
  • There is a discussion about whether the initial reasoning was correct but not comprehensive, with some participants agreeing that it lacked consideration of the non-negativity of the radicand.

Areas of Agreement / Disagreement

Participants express differing views on the correct conditions for continuity, with some asserting that the initial reasoning was flawed while others believe it was partially correct. The discussion remains unresolved regarding the comprehensive conditions for continuity.

Contextual Notes

Participants highlight the importance of ensuring the radicand is non-negative and the implications of manipulating inequalities. There is a lack of consensus on the correct interpretation of the conditions for continuity.

tmt1
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I have this function

$$\frac{e^{sinx}}{4 - \sqrt{x^2 - 9}}$$

And I need to find all the values for which this function is continuous.

So I do

$$4 - \sqrt{x^2 - 9} \ne 0$$

$$ \sqrt{x^2 - 9} \ne 4 $$

$$ x^2 - 9 \ne 16 $$

$$ x^2 \ne 7 $$

And therefore, the function is not valid where

$$ x \ne +/- \sqrt{7} $$

However, this appears to be completely wrong. Why is my reasoning wrong?
 
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First, I would look at:

$$x^2-9\ge0$$

This gives us:

$$(-\infty,-3]\,\cup\,[3,\infty)$$

Next, look at

$$\sqrt{x^2-9}\ne4$$

$$x^2\ne25$$

$$|x|\ne5$$

$$(-\infty,-5)\,\cup\,(-5,5)\,\cup\,(5,\infty)$$

And so, we find:

$$(-\infty,-5)\,\cup\,(-5,-3]\,\cup\,[3,5)\,\cup\,(5,\infty)$$
 
MarkFL said:
First, I would look at:

$$x^2-9\ge0$$

This gives us:

$$(-\infty,-3]\,\cup\,[3,\infty)$$

Next, look at

$$\sqrt{x^2-9}\ne4$$

$$x^2\ne25$$

$$|x|\ne5$$

$$(-\infty,-5)\,\cup\,(-5,5)\,\cup\,(5,\infty)$$

And so, we find:

$$(-\infty,-5)\,\cup\,(-5,-3]\,\cup\,[3,5)\,\cup\,(5,\infty)$$

So what I had was correct but not comprehensive?
 
tmt said:
So what I had was correct but not comprehensive?

No, you took:

$$x^2-9\ne16$$

And added 9 to the left side while subtracting 9 from the right side. You also did not require the radicand to be non-negative. :)
 
tmt said:
I have this function

$$\frac{e^{sinx}}{4 - \sqrt{x^2 - 9}}$$

And I need to find all the values for which this function is continuous.

So I do

$$4 - \sqrt{x^2 - 9} \ne 0$$

$$ \sqrt{x^2 - 9} \ne 4 $$

$$ x^2 - 9 \ne 16 $$

$$ x^2 \ne 7 $$
No, if $x^2- 9\ne 16$ then $x^2= x^2- 9+ 9= 16+ 9= 25$, not 16- 9= 7.

And therefore, the function is not valid where

$$ x \ne +/- \sqrt{7} $$

However, this appears to be completely wrong. Why is my reasoning wrong?
 

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