## Defined integral, but one limit needs to be found

## Defined integral, but one limit needs to be found

(OP)

Hi guys!

Need a little help couse Mathcad doesnt allow me to deine the integral limit as the unknown.

Simple egsample:

integral of "x dx" with limits "a=0 and b=5".

The solution is 12.5

How to reverse the situation so that a=0, b=unknown and provide the previous result of 12.5?

I want Mathcad to find the b value.

How to do this?

Thanx

Need a little help couse Mathcad doesnt allow me to deine the integral limit as the unknown.

Simple egsample:

integral of "x dx" with limits "a=0 and b=5".

The solution is 12.5

How to reverse the situation so that a=0, b=unknown and provide the previous result of 12.5?

I want Mathcad to find the b value.

How to do this?

Thanx

## RE: Defined integral, but one limit needs to be found

TTFN

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## RE: Defined integral, but one limit needs to be found

Is that a command inside Mathcad or something else?

## RE: Defined integral, but one limit needs to be found

## RE: Defined integral, but one limit needs to be found

## RE: Defined integral, but one limit needs to be found

How to use the result you get?

Im asking this becasue if I have even the simpliest equation like 2x+3=0, in Mathcad I would get -3/2 using the "solve for x".

But how to use the x value (-3/2) for your further calculations?

## RE: Defined integral, but one limit needs to be found

Anyother ideas?

## RE: Defined integral, but one limit needs to be found

That would depend on what you're doing, wouldn't it? Presumably, x is something you needed. If you didn't need the solution, then there wouldn't be any point in solving for it, would there?

TTFN

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## RE: Defined integral, but one limit needs to be found

Something on "root" function?

## RE: Defined integral, but one limit needs to be found

TTFN

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## RE: Defined integral, but one limit needs to be found

AnaAnt: What you have to do is --- x:=1 (or something) then Given [CR] 2*x+3:=0 [CR] x:=Find(x). After Given you have to use [CRTL]= just like before.## RE: Defined integral, but one limit needs to be found

## RE: Defined integral, but one limit needs to be found

One more question on root function in MATHCAD.

Plase look at the file attached.

When I try to calculate t(x)=0 and find the the x value "by hande" I get an quadriatic equation with x1 and x2.

Using the root function in Mathcad I always get warning message saying "divide by zero"

What am I doing wrong?

Thank you.

## RE: Defined integral, but one limit needs to be found

Look at your function - what happens for x=0? (Tip: look inside the square brackets ).

So replace the 0 for something like 10^-2 mm (you need to add the unit) and you get 135.017mm.

As an alternative you can use root another way:

x:=1m // guess value needed

z:=root(t(x),x)

## RE: Defined integral, but one limit needs to be found

Peter Nachtwey

Delta Computer Systems

http://www.deltamotion.com

## RE: Defined integral, but one limit needs to be found

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## RE: Defined integral, but one limit needs to be found

^2, otherwise this would mean you have a corrupt copy of mathcad## RE: Defined integral, but one limit needs to be found

Occupant above gave an example that works when there is one undefined variable ie. C1 := Find(C1) but I can't get it to work with 2 unknowns.

Tried something like this C1,C2 := Find (C1,C2) ..... or defining them separately C1 := Find(C1) C2 := Find(C2). It wont solve when I break it up.

## RE: Defined integral, but one limit needs to be found

You can extract values from vectors and matrices by using array subscripts. For example (and asusming

ORIGIN=0), if you haveRes:=Find(C1,C2)=[C1 C2], you can getC1out of the result vector by usingRes[0=and you can getC2by usingRes[1=. The "[" keystroke gets you the array subscript. IfORIGIN=1, then use1and2as your array subscripts.==========

"Is it the only lesson of history that mankind is unteachable?"

--Winston S. Churchill

## RE: Defined integral, but one limit needs to be found

## RE: Defined integral, but one limit needs to be found