Please help me solving this equation ...: )

[Guest]

I have this equation :
(1/Do^4)*(T4+T2/Do)=T1-T3
T1, T2, T3 and T4 are known.
I need to find Do.

How may I solve this using EXCEL ?
Thanks,

 

[BenjieLop]

I have this equation :
(1/Do^4)*(T4+T2/Do)=T1-T3
T1, T2, T3 and T4 are known.
I need to find Do.

How may I solve this using EXCEL ?
Thanks,

One way is to algebraically manipulate your equation so that your
unknown, Do, is on one side of the equation and all your knowns are on
the other side.

By doing so, you will come up with the following --

Do = ((T4+T2)/(T1-T3))^(1/5)

Translating this in Excel, enter this formula in Cell B1

B1 = ((A4+A2)/(A1-A3))^(1/5)

where cell B1 = represents your Do
A1 is where you enter the value of T1
A2 is where you enter the value of T2
A3 is where you enter the value of T3
A4 is where you enter the value of T4

Regards.

 

[Guest]

Hi,

The equation translates into the following 5th order polynomial,

(T3-T1)*Do^5+T4*Do+T2 = 0

and hence, in principle, will have 5 solutions for Do (all real values, or
some real and some imaginary values).

You could use "Solver" to find a solution for Do (for this "Solver" add-in
should have been installed).

Enter the values of T1, T2, T3, and T4 in cells A1, A2, A3, and A4.
In a cell, say B1, enter some guess value for Do (if you have a rough idea
of what Do should be around, enter that value as the guess value; otherwise,
enter 1 and hope it works!). In B2, enter the following formula:

=(1/B1^4)*(A4+A2/B1)-A1+A3 and ENTER. Then


"Tools" --> "Solver" --> "Set Target Cell:" B2, check "Value of:" and
enter 0, "By Changing Cells:" B1 --> "Solve"

Solver will optimize the value in B1 to make B2 equal to zero (or an
extremely small value that can be deemed as zero).
If B2 doesn't become close to zero, try with a different initial guess value
in B1.

Regards,
B. R. Ramachandran

 

[BenjieLop]

Joe,

I misread the second factor in your equation -- (T4 + T2/Do) -- hence I
gave you the wrong solution. I read the equation too carelessly and I
ASSUMED it was something like (T4 + T2)/Do. I apologize for this
oversight.

B.R. Ramachandran's solution is the more accurate one.

Regards.