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Simplify the expression

  • Thread starter frosty8688
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  • #1
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1. Simplify the derivative



2. [itex] y = \frac{\sqrt{1-x^{2}}}{x}[/itex]



3. [itex] f'(x) = \frac{x*\frac{-2x}{2\sqrt{1-x^{2}}}-\sqrt{1-x^{2}}}{x^{2}}=\frac{-x^{2}-\sqrt{1-x^{2}}}{x^{2}\sqrt{1-x^{2}}}[/itex] I just don't know how to simplify this further.
 

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  • #2
SammyS
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1. Simplify the derivative

2. [itex] y = \frac{\sqrt{1-x^{2}}}{x}[/itex]

3. [itex] f'(x) = \frac{x*\frac{-2x}{2\sqrt{1-x^{2}}}-\sqrt{1-x^{2}}}{x^{2}}=\frac{-x^{2}-\sqrt{1-x^{2}}}{x^{2}\sqrt{1-x^{2}}}[/itex] I just don't know how to simplify this further.
You simplified ##\displaystyle \ \frac{\displaystyle x\frac{-2x}{2\sqrt{1-x^{2}}}-\sqrt{1-x^{2}}}{x^{2}} \ ## incorrectly.
 
  • #3
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So it would be -x[itex]^{2}[/itex] over the square root. So how do I find the second derivative of [itex]\frac{\frac{-x^{2}}{\sqrt{1-x^{2}}}-\sqrt{1-x^{2}}}{x^{2}}[/itex] Do I use the product rule or quotient rule. Which is easier?
 
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  • #4
SammyS
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Multiply by ##\displaystyle \ \frac{\sqrt{1-x^2}}{\sqrt{1-x^2}} \ .##
 
  • #5
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Multiply by ##\displaystyle \ \frac{\sqrt{1-x^2}}{\sqrt{1-x^2}} \ .##
I already did that and came out with [itex] \frac{-1}{x^{2}\sqrt{1-x^{2}}}[/itex]
 
  • #6
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How do I take the second derivative?
 
  • #7
haruspex
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How do I take the second derivative?
You can use the quotient rule. To differentiate the denominator use the product rule. Alternatively, rewrite it as a product of two terms with negative exponents and just use the product rule.
 
  • #8
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Here is what I have [itex]\frac{\frac{-x}{\sqrt{1-x^{2}}}-\frac{x^{3}}{(1-x^{2})^{3/2}}} x^{2} + \frac{2}{x^{3}}[/itex] The squared on the top is supposed to go with the x on the bottom.
 
  • #9
SammyS
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Here is what I have [itex]\frac{\frac{-x}{\sqrt{1-x^{2}}}-\frac{x^{3}}{(1-x^{2})^{3/2}}} x^{2} + \frac{2}{x^{3}}[/itex] The squared on the top is supposed to go with the x on the bottom.
You mean [itex]\displaystyle \ \ \frac{\displaystyle \frac{-x}{\sqrt{1-x^{2}}}-\frac{x^{3}}{(1-x^{2})^{3/2}}} {x^{2}} + \frac{2}{x^{3}}\ \ ?[/itex]

I don't see how that can possibly be correct.

Please show some steps.
 
  • #10
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You mean [itex]\displaystyle \ \ \frac{\displaystyle \frac{-x}{\sqrt{1-x^{2}}}-\frac{x^{3}}{(1-x^{2})^{3/2}}} {x^{2}} + \frac{2}{x^{3}}\ \ ?[/itex]

I don't see how that can possibly be correct.

Please show some steps.
Here is how I got that answer [itex]\frac{\frac{-2x^{3}}{2(1-x^{2})^{3/2}}}+\frac{2x}{2\sqrt{1-x^{2}}}-\frac{2x}{\sqrt{1-x^{2}}}{x^{2}}-2\frac{\frac{-x^{2}}{\sqrt{1-x^{2}}}}-\sqrt{1-x^{2}}{x^{3}} = \frac{\frac{-2x^{3}}{2(1-x^{2})^{3/2}}}-\frac{x}{\sqrt{1-x^{2}}}{x^{2}}-2\frac{\frac{-x^{2}}{\sqrt{1-x^{2}}}}-\sqrt{1-x^{2}}{x^{3}} = \frac{\frac{-x}{\sqrt{1-x^{2}}}}-\frac{x^{3}}{(1-x^{2})^{3/2}}{x^{2}}-2\frac{\frac{-x^{2}}{\sqrt{1-x^{2}}}}-\sqrt{1-x^{2}}{x^{3}}=\frac{\frac{-x}{\sqrt{1-x^{2}}}}-\frac{x^{3}}{(1-x^{2})^{3/2}}{x^{2}}+\frac{2}{x^{3}}[/itex] That is how I got the answer. The + sign in the first part should be in the numerator and the x^2 should be in the denominator. Same thing with the sign in the second half of the first part and the sqrt should be in the numerator with the x^3 on the bottom, same thing in the second part and third part and last part. Sorry it got messed up.
 
  • #11
haruspex
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It doesn't need to be that complicated. Write the first derivative as ##-x^{-2}(1-x^2)^{-\frac 12}## and differentiate using the product rule. Hint: every term in the answer ought to have a factor like ##(1-x^2)^{n-\frac 12}##, some integer n. I'd guess that's how SammyS knew your answer could not be right.
 

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