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/sci/ - Science & Math

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4058760 No.4058760 [Reply] [Original]

3^(x+4) = 5^(3x-1)

How???

>> No.4058770

log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log log

>> No.4058780

>>4058770
I get stuck there.

>> No.4058786

http://www.wolframalpha.com/input/?i=3^%28x%2B4%29+%3D+5^%283x-1%29+

http://www.khanacademy.org/#browse
ctrl+f "log" and find the lesson you need explained.

>> No.4058788

you need to use black magic

elementary algebra is too intricate and advanced for any human being to symbolically solve

>> No.4058793
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4058793

[-4log3 - log5] / [log3 - 3log5]

Did that without touching a pen. This must be how ghandi felt when he first stepped on the moon.

>> No.4058797

>>4058793

what is the pen for?

>> No.4058800
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4058800

>>4058793
>babby thinks anyone needs paper/a writing utensil to solve babby algebra

>> No.4058842

Can someone please give me a step by step solution?

>> No.4058855

taking ln of both sides...

(x+4)ln(3) = (3x-1)ln(5)
xln3 + 4ln3 = 3xln5 - ln5
x(ln3-3ln5) = -4ln3 - ln5
x = -(4ln3 - ln5)/(ln3 - 3ln5)

>> No.4058861

>>4058855
Thanks!

Godammit. I hate that feeling when you see how simple it really is and you aren't able to solve it.

>> No.4058864

messed up when I factored out the negative... should be a + sign somewhere

>> No.4058887

>>4058864
>>4058855
yeah, this is the only wrong line:
x = -(4ln3 - ln5)/(ln3 - 3ln5)
(the last one)
it should be:
x = (-4ln3 - ln5)/(ln3 - 3ln5)
or of course,
x = -(4ln3 + ln5)/(ln3 -3ln5)
or to make it look nice:
x = (4ln3 + ln5)/(3ln5 - ln3)