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#### Albert

##### Well-known member
$\pi\approx3.1416$

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

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

edit :$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$

$Prove: \,\, A < B$

Last edited:

#### Opalg

##### MHB Oldtimer
Staff member
$\pi\approx3.1416$

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

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

$Prove: \,\, A < B$
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.

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 $\pi^2<10.$

#### Albert

##### Well-known member
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.

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 $\pi^2<10.$
sorry ! a typo
the original post has been edited
$B=\dfrac{1}{log_2\pi}+\dfrac{1}{log_{\color{red}5}\pi}$