Solve Natural Logarithm Equation lnx+ ln(x-1) = 1

In summary, the conversation is about solving the equation lnx + ln(x-1) = 1 by using logarithm properties and the quadratic formula. The properties of logarithms can be applied to natural logarithms, and the equation can be rewritten as lnx + ln(x-1) = 1 = ln(x^2-x), which can then be solved using the quadratic formula.
  • #1
PolyFX
31
0

Homework Statement



lnx+ ln(x-1) = 1

solve each equation for x

Homework Equations



ln(e^x) = x
e^lnx = x

The Attempt at a Solution



x + (x-1) = e^1 [==> using ln(e^x) = x]
from this point on, I am stuck because I am having trouble isolating x because of the x that is in the brackets.

-Thanks in advance
 
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  • #2
Remember the logarithm property
ln(a) + ln(b) = ln(ab)
 
  • #3
Bohrok,

Thank you. For some reason I always assumed that the logarithm laws such as log(x/y)= log x-logy etc, could not be applied to natural logarithms. I guess questions like that never really came up.

So using ln(ab) = lna + lnb

I get,

lnx + ln(x-1) = 1
ln(x2-x) = 1

so e1 = x2-x

Am I missing a step? I still cannot isolate x to solve for it. I think I may be jumping in a little too early for the cancellation rule.

-Thanks in advance
 
  • #4
The properties of logarithms work with any positive number base (I believe), at least with most numbers you come across, like 10 and e.

What you have now is a quadratic equation with an x2 term, so use the quadratic formula after you set the equation equal to 0.
 

Related to Solve Natural Logarithm Equation lnx+ ln(x-1) = 1

1. What is a natural logarithm?

A natural logarithm is a mathematical function that is the inverse of the exponential function. It is denoted by ln(x) and is defined as the power to which the number e (approximately 2.718) must be raised to equal a given number.

2. What is the difference between a natural logarithm and a common logarithm?

The main difference between a natural logarithm (ln) and a common logarithm (log) is the base. A natural logarithm has a base of e, while a common logarithm has a base of 10. In other words, ln(x) represents the power to which e must be raised to equal x, while log(x) represents the power to which 10 must be raised to equal x.

3. How do you solve a natural logarithm equation?

To solve a natural logarithm equation, you can use the properties of logarithms to rewrite the equation in a simpler form. Then, you can use algebraic methods to isolate the logarithm and solve for the variable. In the case of lnx+ ln(x-1) = 1, you can combine the two logarithms using the product rule to get ln(x(x-1)) = 1, and then use the definition of a logarithm to get x(x-1) = e. Finally, you can use the quadratic formula to solve for x.

4. What are the possible solutions to the equation lnx+ ln(x-1) = 1?

The possible solutions to this equation will depend on the restrictions of the natural logarithm. Since the domain of ln(x) is x > 0, and the domain of ln(x-1) is x-1 > 0, the possible solutions for this equation are x = 2 and x = e+1.

5. How do you check if a solution to a natural logarithm equation is valid?

To check if a solution to a natural logarithm equation is valid, you can substitute the solution back into the original equation and see if it satisfies the equation. In the case of lnx+ ln(x-1) = 1, you can substitute x = 2 and x = e+1 to see if the equation holds true. If it does, then the solutions are valid.

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