Posted by: jmarlow ® 04/05/2007, 10:49:49 Author Profile eMail author Edit

I have the following equation: 0.001 = (0.0000053/X^0.081) + (0.812/X^0.77) I want to solve for X. Ex. X = ..... It has been some time since I did anything like this and cannot figure it out to save my life, nor have I been able to find any examples online or in my text books. Thank you for your assistance, John

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Re: Math Question - Isolating Variable X
Re: Math Question - Isolating Variable X -- jmarlow	Post Reply	Top of thread	Forum

Posted by: jmarlow ® 04/16/2007, 13:46:31 Author Profile eMail author Edit

Also, I should have mentioned that the value "0.0001" is what needs to be changed. This particular value is determined thru another formula in which I have all of the knowns. I have over 400 values that will need to be used in addition to the "0.0001" and this is why I wanted to rewrite in terms of X.

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Re: Math Question - Isolating Variable X
Re: Math Question - Isolating Variable X -- jmarlow	Post Reply	Top of thread	Forum

Posted by: jmarlow ® 04/16/2007, 13:40:56 Author Profile eMail author Edit

Thank you all for your input. The answer is 122,754.23, not 6025. I appreciate all of your efforts. My question was not to solve for the value of X, I can do this using Excel or an advanced calculator. My question was to solve the equation in terms of "X = ". I want to rewrite the equation in terms of X, isolating this variable on its own. I thought when you had a variable raised to some power you used logarithms, but I cannot figure it out.

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Re: Math Question - Isolating Variable X
Re: Math Question - Isolating Variable X -- jmarlow	Post Reply	Top of thread	Forum

Posted by: dbusb ® 04/10/2007, 12:44:30 Author Profile eMail author Edit

You'll have to use Fourie's series. Two terms will be enough

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Re: Re: Math Question - Isolating Variable X
Re: Re: Math Question - Isolating Variable X -- dbusb	Post Reply	Top of thread	Forum

Posted by: AJH ® 04/12/2007, 15:43:13 Author Profile eMail author Edit

You can put it on Excel. If I read your parentheses correctly, x=6025.

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Re: Re: Re: Math Question - Isolating Variable X by AJH
Re: Re: Re: Math Question - Isolating Variable X -- AJH	Post Reply	Top of thread	Forum

Posted by: vicky612 ® 04/15/2007, 02:04:33 Author Profile eMail author Edit

hi AJH, Your solution for the equation interest me.i did try using excel but cant manage to.do u mind guide me or attach the copy of ur excel so that i can refer to the formula and method you went through.thank you in advance.

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Re: Re: Re: Re: Math Question - Isolating Variable X by AJH
Re: Re: Re: Re: Math Question - Isolating Variable X by AJH -- vicky612	Post Reply	Top of thread	Forum

Posted by: AJH ® 04/15/2007, 16:43:10 Author Profile eMail author Edit

In box A1, type in: x= In box A2, type in the following (or cut and paste from this post): =(0.0000053/(B1^0.081))+(0.812/(B1^0.77)) You can input different attempts for X in box B1 until your answer in box A2 comes out to be 0.001. When you input the value 6025 into box B1, your output in box A2 should be 0.001.

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Re: Re: Re: Re: Re: Math Question -it works.thank you.
Re: Re: Re: Re: Re: Math Question - Isolating Variable X by AJH -- AJH	Post Reply	Top of thread	Forum

Posted by: vicky612 ® 04/15/2007, 21:14:08 Author Profile eMail author Edit

thanks alot.it works perfectly.

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Re: Re: Re: Re: Re: Re: Math Question -it works.thank you.
Re: Re: Re: Re: Re: Re: Math Question -it works.thank you. -- vicky612	Post Reply	Top of thread	Forum

Posted by: swearingen ® 04/16/2007, 08:17:54 Author Profile eMail author Edit

Excel's Goal Seek function (under the Tools menu) works great in these cases as well. If the equation is typed in as above, then when you hit Goal Seek you would enter: B2 into "Set cell" 0 into "Value" B1 into "By changing cell" Hit enter twice and you've got your answer.

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