Prove A < B with Log Inequality $\pi\approx3.1416$

In summary, we have an interesting problem where we need to prove that $A < B$ with given values of $\pi$, $A$, and $B$. Using the relation $\log_ab = \dfrac{\ln b}{\ln a}$, we can rewrite the equations to get $A = \dfrac{\ln 360}{\ln 19}$ and $B = \dfrac{\ln 10}{\ln\pi}$. By plugging in the value of $\pi\approx3.1416$, we get $A\approx 1.999$ and $B\approx 1.565$. However, if we redefine $B$ as $B=\dfrac{1}{log_
  • #1
Albert1
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$\pi\approx3.1416$

$A=\dfrac{1}{log_5 19}+\dfrac{2}{log_3 19}+\dfrac{3}{log_2 19}$

$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_3\pi}$

edit :$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$
$Prove: \,\, A < B$
 
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  • #2
Albert said:
$\pi\approx3.1416$

$A=\dfrac{1}{log_5 19}+\dfrac{2}{log_3 19}+\dfrac{3}{log_2 19}$

$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_3\pi}$

$Prove: \,\, A < B$
Is this correct? My calculator gives $A\approx 1.999$ and $B\approx 1.565$. If you define $B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$ then you get $B\approx 2.011$, which makes for a more interesting problem.

[sp]Using the relation $\log_ab = \dfrac{\ln b}{\ln a}$, you find that $A = \dfrac{\ln 360}{\ln 19} <\dfrac{\ln 361}{\ln 19} =2$ (because $361 = 19^2$). But, using my definiton of $B$, $B = \dfrac{\ln 10}{\ln\pi} > 2$ because $\pi^2<10.$[/sp]
 
  • #3
Opalg said:
Is this correct? My calculator gives $A\approx 1.999$ and $B\approx 1.565$. If you define $B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$ then you get $B\approx 2.011$, which makes for a more interesting problem.

[sp]Using the relation $\log_ab = \dfrac{\ln b}{\ln a}$, you find that $A = \dfrac{\ln 360}{\ln 19} <\dfrac{\ln 361}{\ln 19} =2$ (because $361 = 19^2$). But, using my definiton of $B$, $B = \dfrac{\ln 10}{\ln\pi} > 2$ because $\pi^2<10.$[/sp]
sorry ! a typo :eek:
the original post has been edited
$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$
and your solution is :cool:
 
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FAQ: Prove A < B with Log Inequality $\pi\approx3.1416$

1. What is the basic concept of proving A < B with Log Inequality?

The basic concept is to use logarithms to simplify the comparison of two numbers, A and B, by converting them into exponential form. This allows for an easier comparison and proof of A < B.

2. How does the use of logarithms help in proving A < B with Log Inequality?

Logarithms help by converting the numbers into exponential form, which makes it easier to compare them. This is because logarithms have the property that they can turn multiplication and division into addition and subtraction, respectively.

3. Can you provide an example of using Log Inequality to prove A < B?

Sure, let's say we want to prove that 2 < 3. We can use the logarithm base 10 to convert both numbers into exponential form: 10^1 < 10^2. Since the base is the same, we can simply compare the exponents, which in this case shows that 1 < 2. Therefore, we have proven that 2 < 3.

4. Are there any limitations to using Log Inequality to prove A < B?

Yes, there are some limitations. Log Inequality can only be used when the base of the logarithm is the same for both numbers. Also, it cannot be used to compare negative numbers.

5. How does the approximation of $\pi \approx 3.1416$ come into play when proving A < B with Log Inequality?

The approximation of $\pi \approx 3.1416$ is used when the numbers being compared are related to circles or circular shapes. This is because the concept of logarithms was originally developed to solve problems related to circles, and the value of $\pi$ is often involved in these calculations.

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