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10-03-2000
03:00 AM

10-03-2000
03:00 AM

Solving 2 eqns, eliminate parameter

How can Mathcad solve this, which is simple to do by hand:

The inital problem is to find R given D and h, for

R*2*sin(x) = D

R*(1-cos x) = h

The trick is to elinimate x! I can't do it.

To simplify we can write

R*2*x = D

R*x^2/s = h

Even then I dont see how to get Mathcad to find R.

I tried a vector of 2 equations and solve,R-->R(solve for R,x. I got a mysterious line: R = 0.556 K

which makes no sense.

Incidentally, my success at using solve blocks runs about 30%. There must be rules I don't know about.

John C.Polasek

The inital problem is to find R given D and h, for

R*2*sin(x) = D

R*(1-cos x) = h

The trick is to elinimate x! I can't do it.

To simplify we can write

R*2*x = D

R*x^2/s = h

Even then I dont see how to get Mathcad to find R.

I tried a vector of 2 equations and solve,R-->R(solve for R,x. I got a mysterious line: R = 0.556 K

which makes no sense.

Incidentally, my success at using solve blocks runs about 30%. There must be rules I don't know about.

John C.Polasek

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10-03-2000
03:00 AM

10-03-2000
03:00 AM

Solving 2 eqns, eliminate parameter

I solved it right after I posted. It's not a solve block problem. I used Sym/Var/Solve on x, then Sym/Var/Subst into the other x, then Sym/Var/Solve to get the answer to either version.

I don't believe the Var Subst is highlighted in the book MCad 8.

John C. Polasek

I don't believe the Var Subst is highlighted in the book MCad 8.

John C. Polasek

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10-04-2000
03:00 AM

10-04-2000
03:00 AM

Solving 2 eqns, eliminate parameter

John,

The R = 0.556.K comes from Mathcad's built-in units where R is the rankine temperature scale and K is the kelvin scale. This confusion between variables and units frequently arises in Mathcad and I have requested several times in the past that units and variables in Mathcad should have different tags by default. This should not be hard as the constructs are there with the existing tags. Maybe the next release, or even service pack?

-James Lamb

The R = 0.556.K comes from Mathcad's built-in units where R is the rankine temperature scale and K is the kelvin scale. This confusion between variables and units frequently arises in Mathcad and I have requested several times in the past that units and variables in Mathcad should have different tags by default. This should not be hard as the constructs are there with the existing tags. Maybe the next release, or even service pack?

-James Lamb