Here's the question you clicked on:
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A certain radioactive element decays according to N=No e ^-kt. If 50% of the original element sample remains after 9 days, what is the decay rate?
you know if \(t=9\) you have half of what you started with set \[e^{9k}=.5\] and solve for \(k\)
you got this? solve in two steps only
how do you solve for k?
1) write in equivalent logarithmic form (take the log) 2) divide by 9
\[e^{9k}=.5\iff 9k=\ln(.5)\iff k=\frac{\ln(.5)}{9}\]
then if you want a decimal, use a calculator
i have no idea what that means haha. so is it: k= .1831?
wait is ln the button on the calculator for e?
http://www.wolframalpha.com/input/?i=ln%28.5%29%2F9 usually \(ln\) is the button and \(e\) requires the shift key
ok, so i have to use the shift key right? i tried doing e ^.5 which was 1.64 and then divide that by 9 which was .1831
oh, the link helped. sorry we didn't learn this yet so I have no idea what im talking about
so the rate is k= -7.7 x 10 ^-2