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Nesterboy [21]
3 years ago
15

I guess I'm lacking in differential equations. I couldn't solve this question. Can you help me?

Mathematics
2 answers:
Sonja [21]3 years ago
8 0

Answer:

See Explanation.

General Formulas and Concepts:

<u>Pre-Algebra</u>

  • Equality Properties
  • Reciprocals

<u>Algebra II</u>

  • Log/Ln Property: ln(\frac{a}{b} ) = ln(a) - ln(b)

<u>Calculus</u>

Derivatives

Basic Power Rule:

  • f(x) = cxⁿ
  • f’(x) = c·nxⁿ⁻¹

Chain Rule: \frac{d}{dx}[f(g(x))] =f'(g(x)) \cdot g'(x)

Derivative of Ln: \frac{d}{dx} [ln(u)] = \frac{u'}{u}

Step-by-step explanation:

<u>Step 1: Define</u>

ln(\frac{2x-1}{x-1} )=t

<u>Step 2: Differentiate</u>

  1. Rewrite:                                                                                                         t = ln(\frac{2x-1}{x-1})
  2. Rewrite [Ln Properties]:                                                                                 t = ln(2x-1) - ln(x - 1)
  3. Differentiate [Ln/Chain Rule/Basic Power Rule]:                                         \frac{dt}{dx} = \frac{1}{2x-1} \cdot 2 - \frac{1}{x-1} \cdot 1
  4. Simplify:                                                                                                          \frac{dt}{dx} = \frac{2}{2x-1} - \frac{1}{x-1}
  5. Rewrite:                                                                                                          \frac{dt}{dx} = \frac{2(x-1)}{(2x-1)(x-1)} - \frac{2x-1}{(2x-1)(x-1)}
  6. Combine:                                                                                                       \frac{dt}{dx} = \frac{-1}{(2x-1)(x-1)}
  7. Reciprocate:                                                                                                  \frac{dx}{dt} = -(2x-1)(x-1)
  8. Distribute:                                                                                                         \frac{dx}{dt} = (1-2x)(x-1)
zubka84 [21]3 years ago
3 0

Answer:

See below.

Step-by-step explanation:

We are given \displaystyle ln \Big ( \frac{2x-1}{x-1} \Big ) = t and we want to find the first derivative of this function.

We can use the derivative of any function inside a natural log, denoted by \displaystyle \frac{d}{dx} \text{ln} \ u =   \frac{\frac{d}{dx} u}{u}, where u represents any function.

Let's take the derivative of the whole function with respect to x. This will look like:

  • \displaystyle \frac{d}{dx} \displaystyle \Big [ ln \Big ( \frac{2x-1}{x-1} \Big ) = t \Big ] =   \frac{\frac{d}{dx} (\frac{2x-1}{x-1}) }{\frac{2x-1}{x-1} } = \frac{dt}{dx}

Let's take the derivative of the inside function, \displaystyle \frac{2x-1}{x-1}, first. We will need the quotient rule, which is:

  • \displaystyle \frac{d}{dx} \Big [ \frac{f(x)}{g(x)} \Big] = \frac{g(x) \cdot \frac{d}{dx}f(x)-f(x)\cdot \frac{d}{dx}g(x)  }{[g(x)]^2}

Here we have f(x) = 2x - 1 and g(x) = x - 1. Let's plug these values into the formula above:

  • \displaystyle \frac{d}{dx} \Big [ \frac{2x-1}{x-1} \Big ] = \frac{[(x-1)\cdot 2 ] - [(2x-1) \cdot 1]}{(x-1)^2}  
  • \displaystyle \frac{d}{dx} \Big [ \frac{2x-1}{x-1} \Big ] = \frac{2x-2-2x+1}{(x-1)^2}
  • \displaystyle \frac{d}{dx} \Big [ \frac{2x-1}{x-1} \Big ] = \frac{-1}{(x-1)^2}

Now, we can substitute this back into the original equation for the derivative of the entire function.

  • \displaystyle  \frac{dt}{dx} = \frac{\frac{-1}{(x-1)^2} }{\frac{2x-1}{x-1} }  

Multiply the numerator by the reciprocal of the denominator.

  • \displaystyle \frac{dt}{dx} =  \frac{-1}{(x-1)^2} \cdot \frac{x-1}{2x-1}

The (x - 1)'s cancel out and we are left with:

  • \displaystyle \frac{dt}{dx} =  \frac{-1}{(x-1)} \cdot \frac{1}{2x-1}

This can be further simplified to a single fraction:

  • \displaystyle \frac{dt}{dx} =\frac{-1}{(x-1)(2x-1)}  

Now we have dt/dx, but we want to find dx/dt. Therefore, we can flip the equation and have it in terms of dx/dt:

  • \displaystyle \frac{dx}{dt} =\frac{(x-1)(2x-1)}{-1}
  • \displaystyle \frac{dx}{dt} =-(x-1)(2x-1)

This can be further simplified to fit the expression the problem gives for dx/dt:

  • \displaystyle \frac{dx}{dt} =(x-1)(1-2x)

This is equivalent to the equation in the problem; therefore, the verification is complete.

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