Core 3 Level Help - Solve ln (2y - 1) = 1 + ln (3 - y)

  • Thread starter CathyLou
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In summary, In summary, Cathy is seeking help with a math problem involving logarithms and identities. Other users provide hints and guidance until Cathy is able to solve the problem. She then asks for help with another problem, and receives assistance in simplifying her solution.
  • #1
CathyLou
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1
Hi.

Could someone please help me with the following question? I would really appreciate any help as I am totally stuck at the moment.

ln (2y - 1) = 1 + ln (3 - y)

Is the answer:

y = (e + 4) / 3 ?

Thank you.

Cathy
 
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  • #2
Nooo. How did you get that?
 
  • #3
Nooo. How did you get that?

Looks like she tried to exponentiate it...which is the incorrect way to solve this problem.
 
  • #4
Hint: Use identities...Ln(x/y) = Ln(x) - Ln(y)
 
  • #5
Dick said:
Nooo. How did you get that?

I went to 2y = 1 = e^1 + (3 - y)

3y = e^1 + 4

y = e^1 + 4 / 3

Could someone please tell me where I went wrong?

Thank you.

Cathy
 
  • #6
Try using the identity that I just posted.
 
  • #7
e^(1+ln(3-y))=e^1*e^(ln(3-y))=e*(3-y). If you exponentiate a sum, it becomes a product.
 
  • #8
stewartcs said:
Hint: Use identities...Ln(x/y) = Ln(x) - Ln(y)

Thanks for your help.

I now have y = (3e + 1) / (e + 2)

Cathy
 
  • #9
Dick said:
e^(1+ln(3-y))=e^1*e^(ln(3-y))=e*(3-y). If you exponentiate a sum, it becomes a product.

Thank you for your help! :smile:

Cathy
 
  • #10
ln (2y - 1) = 1 + ln (3 - y)

Which gives...

Ln(2y - 1) - Ln(3 - y) = 1

Then using the identity: Ln(x/y) = Ln(x) - Ln(y), gives...

Ln[(2y - 1)/(3 - y)] = 1

Can you take it from here?
 
  • #11
You're welcome.
 
  • #12
Hi.

Could someone please help me with this one too?

Express [(x - 10) / (x - 3)(x + 4)] - [(x - 8) / (x - 3)(2x - 1)] as a single fraction in its simplest form.

I got up to (3x^3 - 20 x^2 + 93x - 126) / (x - 3)(x + 4)(x - 3)(2x - 1) but do not know whether this is correct or what to do next.

Any help would be really appreciated.

Thank you.

Cathy
 
  • #13
That is correct, but it's unnecessarily complicated. The least common denominator is (x-3)*(x+4)*(2x-1). You don't need the second factor of (x-3).
 

Related to Core 3 Level Help - Solve ln (2y - 1) = 1 + ln (3 - y)

1. How do I solve ln (2y - 1) = 1 + ln (3 - y)?

To solve this equation, first combine the logarithms on the right side by using the logarithmic rule ln(a) + ln(b) = ln(ab). This will give you ln[(2y-1)(3-y)] = 1. Then, use the property of logarithms that states ln(b) = x is equivalent to b = e^x. Applying this to our equation, we get (2y-1)(3-y) = e^1, which simplifies to 6y - 3y^2 - 2y + 1 = e. Rearrange the terms to get a quadratic equation in terms of y, solve for y, and check for extraneous solutions.

2. What are the restrictions on the values of y in this equation?

The values of y must satisfy the domain of the natural logarithm function, which is all positive real numbers. In addition, the values of y must also satisfy the restriction that the argument of the logarithm cannot be equal to 0 or negative. This means that 2y - 1 > 0 and 3 - y > 0, or y > 1/2 and y < 3.

3. Can I use a calculator to solve this equation?

Yes, you can use a calculator to solve this equation. Most scientific calculators have a natural logarithm function (ln), and you can use it to check your solutions after solving the equation algebraically.

4. Are there any other ways to solve this equation?

Yes, there are other methods to solve this equation, such as using the properties of logarithms to rewrite the equation in exponential form and then solving for y. You can also try graphing both sides of the equation and finding the intersection point(s). However, the most efficient way to solve this equation is through the algebraic method described in the first question.

5. Can this equation be solved for y using only mental math?

No, this equation cannot be solved using only mental math. It involves using logarithmic rules, properties, and algebraic manipulation, which cannot be done mentally. It is recommended to use a calculator or pen and paper to solve this equation accurately.

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