Exponential equation help (1 Viewer)

[dimzi]

Ok the question is:

Solve 2e^5t = 75 to 3 sig fig's.

I worked it out like this:

log2e^5t = log75
5tlog2e = log75
5t = log75 / log2e

.:. t = 0.509

Now im pretty sure ive got the process right, but im not sure if im putting the log2e in the calculator correctly. I put it in e1 = blah, then blahx2 then I log it. Is that right?

The back of the book says its 0.725

 

[rama_v]

You should usually divide first before taking the log of both sides. ANyway this is how you do it:
2e^5t = 75
e^5t = 75/2
ln e^5t= ln (75/2)
5t= ln(75/2)
t = [ln(75/2)] /5 = 0.725 to three significant figures

 

[dimzi]

Ahh thanks! Didnt know you had to do that, I thought it would just work itself out lol

Thanks again

 

[Marcus Aurelius]

Hahaha. I was doing the same question yesterday cause i've got a test coming up with that stuff in it. I made the same mistake and it took me ages to realise that i should just divide two by 75 from the start. But yeah, since ur using maths in focus the rest of the questions after that question in the exercise use the same principle...