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exponential equation help

hi, I graduated from uni and my maths got very rusty. I stumbled upon an equation that i need to solve at work. The equation looked simple but got me stumped. Can someone help?

a = x0.75 - bx

where a and b are constant. How do I calculate x?

tks.
(edited 10 years ago)
You'll need to use numerical methods, I should think.
Original post by bpeh123
hi, I graduated from uni and my maths got very rusty. I stumbled upon an equation that i need to solve at work. Can someone help?

a = x0.75 - bx

where a and b are constant. How do I calculate x?

tks.


You have a quartic equation so a numerical method would be easiest.

x3=(a+bx)4x^3=(a+bx)^4
The exact solution is pretty horrific!

http://www.wolframalpha.com/input/?i=solve+x%5E3%3D%28a%2Bbx%29%5E4
Reply 4
Avatar for Hasufel
Hasufel
16
you`re too quick Mr M - (I wouldn`t be believed if I said I got that too!)
Original post by Hasufel
you`re too quick Mr M - (I wouldn`t be believed if I said I got that too!)


Turns out Implication was in first.
Reply 6
Avatar for bpeh123
bpeh123
OP
wow that sounds some complicated. what if 0.75 is a constant, ie

a = xk - bx

Is there anything simple so that we can group x on the left?
Reply 7
Avatar for Hasufel
Hasufel
16
interestingly, if you have the pairs of numbers - (sorry, integers!) (you`ll see a pattern):

(a,b)=(−1,2),(−2,3),(−3,4),(−4,5),(−5,6)....(n,∣n∣+1),n∈Z−(a,b) = (-1,2), (-2,3), (-3,4), (-4,5), (-5,6)....(n,|n|+1), n \in \mathbb{Z^{-}}, OR:

(a,b)=(1,−2),(2,−3),(3,−4),(4,−5),(5,−6)....(n,−(n+1)),n∈N(a,b) = (1,-2), (2,-3), (3,-4), (4,-5), (5,-6)....(n,-(n+1)), n \in \mathbb{N},

one of the answers is always x=1...
(edited 10 years ago)
Original post by bpeh123
wow that sounds some complicated. what if 0.75 is a constant, ie

a = xk - bx

Is there anything simple so that we can group x on the left?


What is the actual problem you are trying to solve? You just made it worse!
Reply 9
Avatar for Hasufel
Hasufel
16
Original post by Mr M
Turns out Implication was in first.


Kudos to you both - I`ve ran out of these damn reps!

(I`m off now - battery`s on it`s last legs)
(edited 10 years ago)

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