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Arthurk
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#1
Report Thread starter 14 years ago
#1
Hi, I need urgent help! Can anyone tell me how re-arrange this:

y = 18.655Ln(x) + 46.681

so i can get x when y=50

Any help is really great, thanks
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Daveo
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#2
Report 14 years ago
#2
(Original post by Arthurk)
Hi, I need urgent help! Can anyone tell me how re-arrange this:

y = 18.655Ln(x) + 46.681

so i can get x when y=50

Any help is really great, thanks
Is it just me or is this really easy....i'll wait cos if i'm wrong i'll look silly.
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Nylex
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#3
Report 14 years ago
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(Original post by Arthurk)
Hi, I need urgent help! Can anyone tell me how re-arrange this:

y = 18.655Ln(x) + 46.681

so i can get x when y=50

Any help is really great, thanks
50 = 18.655ln x + 46.681

=> 50 - 46.681 = 18.655ln x

=> (50 - 46.681)/18.655 = ln x

=> ln x = 0.1779...

=> x = e^0.1779...

=> x = 1.194...
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two_headed_monk
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#4
Report 14 years ago
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(Original post by Nylex)
50 = 18.655ln x + 46.681

=> 50 - 46.681 = 18.655ln x

=> (50 - 46.681)/18.655 = ln x

=> ln x = 0.1779...

=> x = e^0.1779...

=> x = 1.194...
wow, i feel really stupid... but then, maths was never my strong suit...
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Arthurk
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#5
Report Thread starter 14 years ago
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Yeah, i feel pretty stupid too now. Is it really that simple? i always thought if you multiplied a natural log it led to some weird shenanigans that meant you couldn't just divide each side by that number. Oh, well, i guess i just like to make things difficult!

Cheers
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Nylex
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#6
Report 14 years ago
#6
(Original post by Arthurk)
Yeah, i feel pretty stupid too now. Is it really that simple? i always thought if you multiplied a natural log it led to some weird shenanigans that meant you couldn't just divide each side by that number. Oh, well, i guess i just like to make things difficult!

Cheers
One of the log rules is: nlog a = log (a^n)

You could also solve for x using that:

50 - 46.681 = 18.655ln x

=> ln (x^18.655) = 50 - 46.681

=> x^18.655 = e^(50 - 46.681)

Then just raise both sides to power 1/18.655.
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