How to solve one variable given two variables and one inequality?












1














So I have a function:



$phi(P) = lvert (1-alpha_2)^P - (1-alpha_1)^Prvert$



It is easy to show that $phi$ is increasing between $0$ and $P_M$, where



$P_{M} = lvert lnbigg(frac{ln(1-alpha_2)}{ln(1-alpha_1)}bigg)/lnbigg(frac{1-alpha_1}{1-alpha_2}bigg)rvert$



and decreasing afterwards.




Assuming $1 > alpha_1 > alpha_2$ > 0, if $P_{M} leq 1$, how could I prove the following?



$alpha_1 > 1-frac{1}{e} > 0.63$




I have stuck here for hours. I think it is a easy step to make it. However, I couldn't figure it out.



Any idea is much appreciated. Thanks!










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  • Please try to make the titles of your questions more informative. For example, Why does $a<b$ imply $a+c<b+c$? is much more useful for other users than A question about inequality. From How can I ask a good question?: Make your title as descriptive as possible. In many cases one can actually phrase the title as the question, at least in such a way so as to be comprehensible to an expert reader. You can find more tips for choosing a good title here.
    – Shaun
    Nov 25 at 4:24
















1














So I have a function:



$phi(P) = lvert (1-alpha_2)^P - (1-alpha_1)^Prvert$



It is easy to show that $phi$ is increasing between $0$ and $P_M$, where



$P_{M} = lvert lnbigg(frac{ln(1-alpha_2)}{ln(1-alpha_1)}bigg)/lnbigg(frac{1-alpha_1}{1-alpha_2}bigg)rvert$



and decreasing afterwards.




Assuming $1 > alpha_1 > alpha_2$ > 0, if $P_{M} leq 1$, how could I prove the following?



$alpha_1 > 1-frac{1}{e} > 0.63$




I have stuck here for hours. I think it is a easy step to make it. However, I couldn't figure it out.



Any idea is much appreciated. Thanks!










share|cite|improve this question
























  • Please try to make the titles of your questions more informative. For example, Why does $a<b$ imply $a+c<b+c$? is much more useful for other users than A question about inequality. From How can I ask a good question?: Make your title as descriptive as possible. In many cases one can actually phrase the title as the question, at least in such a way so as to be comprehensible to an expert reader. You can find more tips for choosing a good title here.
    – Shaun
    Nov 25 at 4:24














1












1








1







So I have a function:



$phi(P) = lvert (1-alpha_2)^P - (1-alpha_1)^Prvert$



It is easy to show that $phi$ is increasing between $0$ and $P_M$, where



$P_{M} = lvert lnbigg(frac{ln(1-alpha_2)}{ln(1-alpha_1)}bigg)/lnbigg(frac{1-alpha_1}{1-alpha_2}bigg)rvert$



and decreasing afterwards.




Assuming $1 > alpha_1 > alpha_2$ > 0, if $P_{M} leq 1$, how could I prove the following?



$alpha_1 > 1-frac{1}{e} > 0.63$




I have stuck here for hours. I think it is a easy step to make it. However, I couldn't figure it out.



Any idea is much appreciated. Thanks!










share|cite|improve this question















So I have a function:



$phi(P) = lvert (1-alpha_2)^P - (1-alpha_1)^Prvert$



It is easy to show that $phi$ is increasing between $0$ and $P_M$, where



$P_{M} = lvert lnbigg(frac{ln(1-alpha_2)}{ln(1-alpha_1)}bigg)/lnbigg(frac{1-alpha_1}{1-alpha_2}bigg)rvert$



and decreasing afterwards.




Assuming $1 > alpha_1 > alpha_2$ > 0, if $P_{M} leq 1$, how could I prove the following?



$alpha_1 > 1-frac{1}{e} > 0.63$




I have stuck here for hours. I think it is a easy step to make it. However, I couldn't figure it out.



Any idea is much appreciated. Thanks!







derivatives inequality boundary-value-problem






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share|cite|improve this question













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edited Nov 25 at 20:20

























asked Nov 25 at 2:50









Wei

162




162












  • Please try to make the titles of your questions more informative. For example, Why does $a<b$ imply $a+c<b+c$? is much more useful for other users than A question about inequality. From How can I ask a good question?: Make your title as descriptive as possible. In many cases one can actually phrase the title as the question, at least in such a way so as to be comprehensible to an expert reader. You can find more tips for choosing a good title here.
    – Shaun
    Nov 25 at 4:24


















  • Please try to make the titles of your questions more informative. For example, Why does $a<b$ imply $a+c<b+c$? is much more useful for other users than A question about inequality. From How can I ask a good question?: Make your title as descriptive as possible. In many cases one can actually phrase the title as the question, at least in such a way so as to be comprehensible to an expert reader. You can find more tips for choosing a good title here.
    – Shaun
    Nov 25 at 4:24
















Please try to make the titles of your questions more informative. For example, Why does $a<b$ imply $a+c<b+c$? is much more useful for other users than A question about inequality. From How can I ask a good question?: Make your title as descriptive as possible. In many cases one can actually phrase the title as the question, at least in such a way so as to be comprehensible to an expert reader. You can find more tips for choosing a good title here.
– Shaun
Nov 25 at 4:24




Please try to make the titles of your questions more informative. For example, Why does $a<b$ imply $a+c<b+c$? is much more useful for other users than A question about inequality. From How can I ask a good question?: Make your title as descriptive as possible. In many cases one can actually phrase the title as the question, at least in such a way so as to be comprehensible to an expert reader. You can find more tips for choosing a good title here.
– Shaun
Nov 25 at 4:24















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