log-5x=log (10-3x)

Question

log-5x=log (10-3x)

slaaibak · Answer

$$\log (-5x) = \log(10 - 3x)$$

Is that the question?

anonymous · Answer

yeah haha my bad

slaaibak · Answer

Do you agree that

 -5x = 10 - 3x ?

anonymous · Answer

x=-5?

anonymous · Answer

i understand that one now though. but another one of the questions is log a=og(4a-9) and the answer is supposed to be 3 but i'm getting 2.25

anonymous · Answer

yeah -5 is what i got (:

slaaibak · Answer

I don't think you can have a negative log tho :/ so no real solutions?

anonymous · Answer

but RHS is imaginary!

anonymous · Answer

true

anonymous · Answer

so,no real solution exists.

slaaibak · Answer

log a = log(4a - 9)

Now:

a = 4a - 9
-3a = -9

a = 3

anonymous · Answer

OH dude. i'm dumb. for some reason i was moving it over and changing it to -4a -.- thank you so much !!!!

anonymous · Answer

you are not dumb,silly mistakes happens :-)

anonymous · Answer

(: thanks !

slaaibak · Answer

haha, the mistakes I've made in math are far worse :) Hope this helped!

anonymous · Answer

wait i'm sorry can i ask another question? ( i was absent when this was all being taught) but how would you solve 
-4log3-9m=-4? 
since there's no log on the right side of the equation?

slaaibak · Answer

$$-4\log(3-9m)=-4 $$

?

anonymous · Answer

$$-4\log _{3}-9m=-4$$ (:

slaaibak · Answer

wait, that doesn't make sense.

$$-4\log_3(-9m)=-4 $$

anonymous · Answer

maybe that's how it's supposed to be. it just doesn't show up like that on the worksheet.

slaaibak · Answer

Assuming that's the question:

First divide both side by -4:

$$\log_3(-9m) = 1$$


Now, you need to know this property of logarithms:

$$a^x = b$$

$$\log_a b = x$$

$$a^x = b$$

Now your problem:

$$\log_3(-9m) = 1 \rightarrow 3^1 = -9m$$

$$m={-1 \over 3}$$

anonymous · Answer

WOW. you're great.

slaaibak · Answer

:) Know the laws by heart, and it will be very very easy!

anonymous · Answer

haha i hope so.