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how to solve this equation using excel 2007 and manually................... 50=120π/2.464{a/(0.0 635)+ 1.393+0.667 ln[a/(0.0 635)+ 1.444] }

You have one equation and two unknown variables... you cannot solve it without constraining "a" or "n".

no, i only have variable which is "a". The variable "n" that you have seen actually is not "n" but it is "pai" OR 3.142

Ah, that makes it better. In Excel, you can use the solver add-in. Depending on the version of Excel, it's under Tools or, File/Options/Add-in. In cell A1, put in a starting value for a. In B1, type in your equation, such that it uses the value in A1 for "a". You can use the function pi() to return 3.14159... in Excel, =120*pi()*...

Start up the solver add-in, it's in the menus once you enable the Add-In. In the dialog box, point it you the target cell (B1), tell it to go to a target value (50), select cells to change (A1), then set criteria like >0 to bound Excel's options for the value it puts into A1 while searching for 50 ohms.

As for manually, dust off the algebra book's cobwebs and grab a lot of scratch paper.

What you means by "Start up the solver add-in, it's in the menus once you enable the Add-In"? I did not found what is solver add-in in my excel. Isn't because I'm using the Excel 2007? can you show me with the images (print screen)...please~

First, when faced with any computer-related issue, refer to the following problem-solving method.
Tech Support Cheat Sheet - XKCD
(kidding, but not much... that's pretty much how I operate when faced w/ new problems on a PC)

Second, use Google to find a how-to webpage for most any feature/function in the MS Office suite. I searched for "solver excel 2007" and got a pile of hits, here's the first one:
http://office.microsoft.com/en-us/ex...010021570.aspx

sorry....I forgot to mention you that the problem has been solved...I already get the answer/solution....thanks for your information~

np. When you find a solution, you can click on the "mark thread solved" link to make it clear that there should be no more activity on your thread. It's a nice way to keep the forum "clean".

Now that you know Solver exists, you'll probably find lots of ways to use it... I know I certainly did after it was shown to me