Calculate with 2-3 unknowns - Help please

I

irish634

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Aug 3, 2010
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Hello, I am in need of some assistance from someone smarter than me. Haha.


HELP please

Postby irish634 » Fri Aug 13, 2010 8:31 pm
How do I back calculate to “f”?

? = (L * ?c) / (? * ? * P)

Where:
? = 1.0366
L = 1000
? = 5.8E+08
P = 12.56

?c = (1+(2/ ?)*ATAN(1.4*(?/ ?)^2))
? = 0.07874

? = (1/SQRT(? *f* ? * ?))*39370.07874
? = 1.257E-06

I can solve for f once I figure out how to calculate ? and ?c. So basically I have two unknowns. I am having a hard time trying to figure this out. “f” should work out to approx 1E+09



My second problem to calculate is for ?

? = (L * ?c) / (? * ? * P)

Where:
? = 1.0366
L = 1000
f = 1E+09
P = 12.56

?c = (1+(2/ ?)*ATAN(1.4*(?/ ?)^2))
? = 0.07874

? = (1/SQRT(? *f* ? * ?))*39370.07874
? = 1.257E-06

So in this problem, I need ? to be able to solve for ? and ?c. So there are 3 unknowns here. ? should work out to be about 5.8E+08.

These are obviously a little over my head here. I am tasked to create a program for work… I can code it, just not sure how to solve it. Similar to above, I have no problem solving this if I know all but one unknown.

Thank you for your assistance.
 
irish634 said:
Hello, I am in need of some assistance from someone smarter than me. Haha.


HELP please

Postby irish634 » Fri Aug 13, 2010 8:31 pm
How do I back calculate to “f”?

? = (L * ?c) / (? * ? * P)

Where:
? = 1.0366
L = 1000
? = 5.8E+08
P = 12.56

?c = (1+(2/ ?)*ATAN(1.4*(?/ ?)^2))

? = 0.07874 ? What is this?

? = (1/SQRT(? *f* ? * ?))*39370.07874 ? Is this number correct?
? = 1.257E-06

I can solve for f once I figure out how to calculate ? and ?c. So basically I have two unknowns. I am having a hard time trying to figure this out. “f” should work out to approx 1E+09



My second problem to calculate is for ?

? = (L * ?c) / (? * ? * P)

Where:
? = 1.0366
L = 1000
f = 1E+09
P = 12.56

?c = (1+(2/ ?)*ATAN(1.4*(?/ ?)^2))
? = 0.07874

? = (1/SQRT(? *f* ? * ?))*39370.07874
? = 1.257E-06

So in this problem, I need ? to be able to solve for ? and ?c. So there are 3 unknowns here. ? should work out to be about 5.8E+08.

These are obviously a little over my head here. I am tasked to create a program for work… I can code it, just not sure how to solve it. Similar to above, I have no problem solving this if I know all but one unknown.

Thank you for your assistance.
Click to expand...
 
? = 0.07874 - This is used for surface roughness of a printed circuit board trace. the value is most commonly expressed in microns, but for this I am working in mils. So 2 microns = 0.07874015748 mil


? = (1/SQRT(? *f* ? * ?))*39370.07874 - Yes this is correct. ? is expressed in meters. Usually it's just
? = (1/SQRT(? *f* ? * ?)) but needing to convert to mils I need to multiply by 39370.07874


Now the kicker is:
In this equation:? = (L * ?c) / (? * ? * P) , ? is in meters (without the 39370.07874 multiplier) but to calculate for ?c, both ? and ? need to be in the same units. Doesn't really matter which units (meters, mm, microns, mils, inches) as long as they are both the same.

Basically,
?c should equal approximately 1.578
? should equal approximately 0.08227 in mils
? should equal approximately 2.09E-06 in meters

I am able to figure out the calculations if I only have one unknown, but I'm at a loss here
 
Why don't you repost the whole mess using single letters as variables; like a,b,x,y and the likes.
We're not here to learn how to post weird symbols!
Example:
? = (L * ?c) / (? * ? * P)

a = bc / (def)
 
irish634 said:
Hello, I am in need of some assistance from someone smarter than me. Haha.


HELP please

Postby irish634 » Fri Aug 13, 2010 8:31 pm
How do I back calculate to “f”?

? = (L * ?c) / (? * ? * P) ...............................................................(3)

Where:
? = 1.0366
L = 1000
? = 5.8E+08
P = 12.56

?c = (1+(2/ ?)*ATAN(1.4*(?/ ?)^2))..........................................................(2)
? = 0.07874

? = (1/SQRT(? *f* ? * ?))*39370.07874 .....................................(1)
? = 1.257E-06

There is no "closed-form" solution to this problem.

Assume a value for "f = f[sub:2ls476z2]old[/sub:2ls476z2]"

then calculate ?[sub:2ls476z2]old[/sub:2ls476z2] from (1)

Then calculate ?c using (2)

then calculate ?[sub:2ls476z2]new[/sub:2ls476z2] from (3)

then calculate f[sub:2ls476z2]new[/sub:2ls476z2] using (1)

Repeat till you get desired accuracy

I can solve for f once I figure out how to calculate ? and ?c. So basically I have two unknowns. I am having a hard time trying to figure this out. “f” should work out to approx 1E+09



My second problem to calculate is for ?

? = (L * ?c) / (? * ? * P)

Where:
? = 1.0366
L = 1000
f = 1E+09
P = 12.56

?c = (1+(2/ ?)*ATAN(1.4*(?/ ?)^2))
? = 0.07874

? = (1/SQRT(? *f* ? * ?))*39370.07874
? = 1.257E-06

Follow the same algorism as above

So in this problem, I need ? to be able to solve for ? and ?c. So there are 3 unknowns here. ? should work out to be about 5.8E+08.

These are obviously a little over my head here. I am tasked to create a program for work… I can code it, just not sure how to solve it. Similar to above, I have no problem solving this if I know all but one unknown.

Thank you for your assistance.
Click to expand...

I bet you were one of those computer science student who thought you'll never use algebra again- I met whole bunch of those
 
No not a computer science geek Haha... But yes I never thought I'd use algebra again. I even dug out my old math text book to try to figure this out.

I'll set up the algorithm for the iterations and see what I come up with. Thank you.
 
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