D/dx x(x^2 +1) ^{1 /2}/(x+1) ^{2 /3}

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  • Thread starter karush
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In summary: Now, to find $y$, just substitute into the original equation and simplify. So, in summary, we can find the derivative of $y$ by taking the natural log of both sides, applying the rules of logarithms, implicitly differentiating, and then substituting back into the original equation to solve for $y$.
  • #1
karush
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​$\large{242.q2.1c}$
Find the derivative
$$\displaystyle
y=\frac{x(x^2 +1) ^{1/2}}{(x+1)^{2/3}}$$
I know this is using the quotient rule but can't seem simplify this first
 
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  • #2
karush said:
​$\large{242.q2.1c}$
Find the derivative
$$\displaystyle
y=\frac{x(x^2 +1) ^{1/2}}{(x+1)^{2/3}}$$
I know this is using the quotient rule but can't seem simplify this first

I do not see anything in common . So this cannot be simplified fisrt

you can take it of the form $\frac{u}{v}$ and then u as a product.
 
  • #3

I suggest Logarithmic Differentiation.
 
  • #4
soroban said:

I suggest Logarithmic Differentiation.

I think that's what was intended but missed the lecture on it
 
  • #5
karush said:
I think that's what was intended but missed the lecture on it

Take the natural log of both sides, apply the rules of logs to the right side, then implicitly differentiate. :)
 
  • #6
karush said:
[tex]\text{Find the derivative :}[/tex]
$$\displaystyle
y=\frac{x(x^2 +1) ^{1/2}}{(x+1)^{2/3}}$$

[tex]\text{Take logs: }\; \ln y \;=\;\ln\left[\frac{x(x^2+1)^{\frac{1}{2}}}{(x+1)^{\frac{2}{3}}}\right] \;=\;\ln x + \ln(x^2+1)^{\frac{1}{2}} - \ln(x+1)^{\frac{2}{3}}[/tex]

. .. .. .. . . . [tex]\ln y \;=\;\ln x + \tfrac{1}{2}\ln(x^2+1) - \tfrac{2}{3}\ln(x+1)[/tex]

. . [tex]\frac{y'}{y} \;=\;\frac{1}{x} + \frac{1}{2}\frac{2x}{x^2+1} = \frac{2}{3}\frac{1}{x+1}[/tex]

. . . . [tex]\text{ . . . etc. . . . }[/tex]
 
  • #7
$\displaystyle
\ln y \;=
\;\ln\left[\frac{x(x^2+1)^{\frac{1}{2}}}{(x+1)^{\frac{2}{3}}}\right] \\
=\ln x
+ \frac{1}{2}\ln(x^2+1) - \frac{2}{3}\ln(x+1)$

$\displaystyle
y' =y \left[\frac{1}{x}
+ \frac{x}{x^2+1}
- \frac{2}{3(x+1)}\right]
$

What is $\frac{y'}{y}$ ?
 
Last edited:
  • #8
karush said:
$\displaystyle
\ln y \;=
\;\ln\left[\frac{x(x^2+1)^{\frac{1}{2}}}{(x+1)^{\frac{2}{3}}}\right] \\
=\ln x
+ \frac{1}{2}\ln(x^2+1) - \frac{2}{3}\ln(x+1)$

$\displaystyle
y' =y \left[\frac{1}{x}
+ \frac{x}{x^2+1}
- \frac{2}{3(x+1)}\right]
$

What is $\frac{y'}{y}$ ?

Now that you have solved for $y'$, just substitute for $y$ and you will have the derivative as a function of $x$.
 
  • #9
$\displaystyle \ln y \;=
\;\ln\left[\frac{x(x^2+1)^{\frac{1}{2}}}{(x+1)^{\frac{2}{3}}}\right] \\
=\;\ln x
+ \frac{1}{2}\ln(x^2+1) - \frac{2}{3}\ln(x+1)$

$\displaystyle
y' =\left[\frac{x(x^2+1)^{\frac{1}{2}}}{(x+1)^{\frac{2}{3}}}\right]
\left[\frac{1}{x}
+ \frac{x}{x^2+1}
- \frac{2}{3(x+1)}\right]
$
 
Last edited:

FAQ: D/dx x(x^2 +1) ^{1 /2}/(x+1) ^{2 /3}

1. What does the "d/dx" notation mean in this equation?

The "d/dx" notation represents the derivative of a function with respect to the variable x. It is used to find the rate of change of the function at a specific point.

2. How do I simplify this equation?

To simplify this equation, you can use the power rule for derivatives and the quotient rule. First, use the power rule to find the derivative of the numerator, which will be 3x(x^2+1)^1/2. Then, use the quotient rule to find the derivative of the entire equation, which will be [(2x(x^2+1)^1/2)/(2(x+1)^5/3)] - [(3x(x^2+1)^1/2)/(3(x+1)^4/3)].

3. How do I solve for x in this equation?

This equation does not have a single solution for x because it is a derivative and represents a rate of change. However, you can solve for specific values of x by plugging them into the equation and finding the corresponding rate of change.

4. What is the significance of the exponents in this equation?

The exponents in this equation represent the power to which the number or variable is raised. In this case, they are used to express the derivatives of the functions in the numerator and denominator.

5. Can this equation be used to solve real-world problems?

Yes, this equation can be used to solve real-world problems that involve rates of change, such as finding the velocity of an object or the growth rate of a population. However, it should be noted that this specific equation may not be directly applicable to all real-world scenarios and may need to be modified or combined with other equations to accurately model the problem at hand.

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