C3 Natural Logs Help

Hi,

There are a couple of log questions that I'm stuck on:

2e^x= 3e^-x +5
2lne^x=3lne^-x +ln5
2x= -3x + ln5
5x= ln5
x=0.32 I had a go but I feel like I'm following the wrong steps.

The other one that I'm stuck on is:
ln (2x+1) = lnx+2

Thanks :smile:

Reply 1

richpanda

16

Original post by VioletPhillippo

Hi,

There are a couple of log questions that I'm stuck on:

2e^x= 3e^-x +5
2lne^x=3lne^-x +ln5
2x= -3x + ln5
5x= ln5
x=0.32 I had a go but I feel like I'm following the wrong steps.

The other one that I'm stuck on is:
ln (2x+1) = lnx+2

Thanks :smile:

Use brackets please. I'm not sure if it's 3e^(-x+5) or if it's 3e^(-x) +5

Reply 2

the bear

20

you cannot say log( e^x +e^y ) is the same as logx + logy

Reply 3

davros

16

Original post by VioletPhillippo

Hi,

There are a couple of log questions that I'm stuck on:

2e^x= 3e^-x +5
2lne^x=3lne^-x +ln5
2x= -3x + ln5
5x= ln5
x=0.32 I had a go but I feel like I'm following the wrong steps.

The other one that I'm stuck on is:
ln (2x+1) = lnx+2

Thanks :smile:

As thebear says, it is NOT true that ln(x + y) = ln x + ln y, so your first approach will get you nowhere!

I would suggest multiplying both sides by e^x which will give you a quadratic in e^x.

C3 Natural Logs Help

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