PLEASEHELP ME!

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rachael724

Junior Member
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Sep 14, 2005
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This problem has left me clueless, any direction would help. Thanks!

Radioactive isotopes, as well as solar cells, are used to supply power to space vehicles.The isotope cells gradually lose power due to radioactive decay. On space probe 201, the power output of P watts after t days of use is given by
P(t) = 75e-0.0020t. The probe will shut down when the wattage goes below 35 watts. Correct to the nearest whole day, how many days after launch will the probe shut down?
 
Plug in "35" for "P(t)".

Solve for t.

Round to the nearest whole number.

Eliz.
 
How did you get that? (It is difficult to check work that hasn't been posted.)

When you reply, please clarify the function in question. You have posted:

. . . . .P(t) = 75e - 0.0020t

But this is a highly unusual decay equation. Did you perhaps mean the following?

. . . . .P(t) = 75e<sup>-0.0020t</sup>

(For information on formatting math, please follow the link to "Karl's" page, in the pull-down menu at the top of the page.)

Thank you.

Eliz.
 
\(\displaystyle ln{(e^x)} = x\)

That is, we take natural logs (ln) to "undo" an exponential (base e).
 
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