How Do You Solve Logarithmic Equations Involving Quadratics?

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In summary, the conversation discusses solving the equation logx = 1 + 6/logx by first multiplying both sides by logx to get a quadratic equation. The equation is then solved by using substitution and factoring. The final solutions for x are not 3 and -2, as shown in the conversation, but rather the values that make the quadratic equation equal to 0.
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storoi1990
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Q: Logx = 1 + 6/logx

my attempt so far: Log x^2 = 7

where do i go from here?
 
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How did you obtain this result? Try to multiply the whole equation with logx. You'll arrive at a quadratic equation. Try to use a substitution then.
 
  • #3


storoi1990 said:
Q: Logx = 1 + 6/logx

my attempt so far: Log x^2 = 7

where do i go from here?
Is this [itex]log x= 1+ \frac{6}{log x}[/itex] or [itex]log x= \frac{1+ 6}{log x}[/itex]?

I suspect it is the former because otherwise it would just be written as 7/ log x. But then multiplying log x= 1+ (6/log x) by log x you get (log x)^2= log x+ 6. Let y= log x and that becomes y^2= y+ 6. Solve that quadratic equation for y, then solve log x= y for x.
 
  • #4


yeah it's the last one.

so then i end up with:

y^2-y-6 = 0

x1 = 3 , and x2 = -2

is that the answer?
 
  • #5


storoi1990 said:
yeah it's the last one.
You mean the first one, which is logx = 1 + (6/logx).
storoi1990 said:
so then i end up with:

y^2-y-6 = 0
[\quote]This factors into (y - 3)(y + 2) = 0, so y = 3 or y = -2.

Now, since y = logx, you have logx = 3 or log x = -2.
What are the solutions for x? They are NOT 3 and -2, as you show below.
storoi1990 said:
x1 = 3 , and x2 = -2

is that the answer?
 

FAQ: How Do You Solve Logarithmic Equations Involving Quadratics?

What is a logarithm?

A logarithm is the inverse function of exponentiation. It is used to solve equations where the variable is in the exponent.

What is the base of a logarithm?

The base of a logarithm is the number that is raised to a certain power to get the argument of the logarithm. In this equation, the base is unknown and represented as logx.

What is the process for solving for log x^2 = 7?

To solve for log x^2 = 7, we need to use the properties of logarithms to rewrite the equation as x^2 = 10^7. Then, we can take the square root of both sides to get x = ±√10^7. This can be simplified to x = ±√10 * 10^3, which means x = ±√10 * 1000. Finally, we can simplify further to get x = ±10√10.

What are the possible solutions for log x^2 = 7?

Since we took the square root of both sides, there are two possible solutions for x: x = 10√10 or x = -10√10.

Can this equation be solved without a calculator?

Yes, this equation can be solved without a calculator by using the properties of logarithms and simplifying the equation algebraically. However, using a calculator can help to find the approximate decimal value of the solution.

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