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

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The discussion centers on proving that A is less than B, where A is defined as A = 1/log5(19) + 2/log3(19) + 3/log2(19) and B as B = 1/log2(π) + 1/log5(π). Calculations show A is approximately 1.999 and B is approximately 1.565 with the original definition of B, but redefining B leads to B being approximately 2.011, which complicates the proof. The relationship log_ab = ln(b)/ln(a) is used to analyze A and B further, indicating that A < 2 and B > 2 under certain conditions. The conversation highlights the nuances in defining B and the implications for the inequality A < B.
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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 :$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$
$Prove: \,\, A < B$
 
Last edited:
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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]
 
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 :o
the original post has been edited
$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$
and your solution is :cool:
 
Last edited:
Here is a little puzzle from the book 100 Geometric Games by Pierre Berloquin. The side of a small square is one meter long and the side of a larger square one and a half meters long. One vertex of the large square is at the center of the small square. The side of the large square cuts two sides of the small square into one- third parts and two-thirds parts. What is the area where the squares overlap?

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