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The equation has one unknown, but appear on both sides of the equation:
A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)] THe only unknown that need to be solved is A. B, C, D, and E are known variables. How to solve? |
#2
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san2000 -
Maybe you could use Goal Seek (to change A by trying to set the difference between the left and right sides of your equation to the value zero). For example, using the values B=2, C=3, D=4, and E=5, I entered the following in cell B1: =A1+2/2-SQRT(3/4)*((5-A1)^(3/2))/((A1-2)^(1/2)) Then I entered a tentative value of 3 in cell A1. Then I chose Tools | Goal Seek, and used Set Cell B1, To Value 0 (zero), and By Changing Cell A1. For more precision, choose Tools | Options | Calculation, and enter a smaller value for Maximum Change. You do not need to check the Iterations box. - Mike http://www.mikemiddleton.com "san2000" wrote in message ... The equation has one unknown, but appear on both sides of the equation: A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)] THe only unknown that need to be solved is A. B, C, D, and E are known variables. How to solve? |
#3
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Thanks Mike. I use Goal Seek, but find out that it can only apply one cell
at a time. Is there a way to make the process faster? Will Macro helps in this situation? I'm not familar with Macro at all. Any help would be great. Thanks in advance. "Mike Middleton" wrote: san2000 - Maybe you could use Goal Seek (to change A by trying to set the difference between the left and right sides of your equation to the value zero). For example, using the values B=2, C=3, D=4, and E=5, I entered the following in cell B1: =A1+2/2-SQRT(3/4)*((5-A1)^(3/2))/((A1-2)^(1/2)) Then I entered a tentative value of 3 in cell A1. Then I chose Tools | Goal Seek, and used Set Cell B1, To Value 0 (zero), and By Changing Cell A1. For more precision, choose Tools | Options | Calculation, and enter a smaller value for Maximum Change. You do not need to check the Iterations box. - Mike http://www.mikemiddleton.com "san2000" wrote in message ... The equation has one unknown, but appear on both sides of the equation: A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)] THe only unknown that need to be solved is A. B, C, D, and E are known variables. How to solve? |
#4
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san2000 -
Your description of your problem specifically stated there was only one unknown, so Goal Seek is appropriate. If you have several unknowns, Excel's Solver may be more appropriate. In general, a macro (VBA) will not be faster than Excel's built-in features. - Mike "san2000" wrote in message ... Thanks Mike. I use Goal Seek, but find out that it can only apply one cell at a time. Is there a way to make the process faster? Will Macro helps in this situation? I'm not familar with Macro at all. Any help would be great. Thanks in advance. "Mike Middleton" wrote: san2000 - Maybe you could use Goal Seek (to change A by trying to set the difference between the left and right sides of your equation to the value zero). For example, using the values B=2, C=3, D=4, and E=5, I entered the following in cell B1: =A1+2/2-SQRT(3/4)*((5-A1)^(3/2))/((A1-2)^(1/2)) Then I entered a tentative value of 3 in cell A1. Then I chose Tools | Goal Seek, and used Set Cell B1, To Value 0 (zero), and By Changing Cell A1. For more precision, choose Tools | Options | Calculation, and enter a smaller value for Maximum Change. You do not need to check the Iterations box. - Mike http://www.mikemiddleton.com "san2000" wrote in message ... The equation has one unknown, but appear on both sides of the equation: A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)] THe only unknown that need to be solved is A. B, C, D, and E are known variables. How to solve? |
#5
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Hi. Just some thoughts.
With multiple square roots, it brings to mind multiple solutions. Also, note that it ae, or a<b, then you will be working with Complex numbers. (Sqrt of negative numbers). Does this constraint hold? b<a<e? If C is the opposite sign of D, you will have a sqrt of a negative number as well. One additional method could be the Newton Equation. Goal Seek works great, but can be limited in its accuracy. However, you can loop a few more times in your own function. This isn't fancy, and it doesn't have much error checking. Here's a simple example using Mike's numbers... Sub TestIt() Debug.Print Fx(2, 3, 4, 5) End Sub Function Fx(b, c, d, e) Dim K1 Dim K2 Dim a Dim Num Dim Den Dim Last K1 = b / 2 K2 = Sqr(c / d) Last = 0 a = (b + e) / 2 'Middle Do While Last < a Last = a Num = a + K1 - ((K2 * (e - a) ^ (3 / 2)) / Sqr(a - b)) Den = ((Sqr(e - a) * (2 * a - 3 * b + e) * K2) / _ (a - b) ^ (3 / 2) + 2) / 2 a = a - Num / Den Debug.Print a If a e Then a = e If a < b Then a = b + 0.00001 Loop End Function Returns a = 2.68510380165928 which checks... -- HTH :) Dana DeLouis Windows XP & Office 2003 "san2000" wrote in message ... The equation has one unknown, but appear on both sides of the equation: A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)] THe only unknown that need to be solved is A. B, C, D, and E are known variables. How to solve? |
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