×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Defined integral, but one limit needs to be found2

## 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
Replies continue below

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

(OP)
"solve block"
Is that a command inside Mathcad or something else?

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

(OP)
...and you like to drink wich beer and how much?

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

(OP)
One more question, and thenx for the previous answer.
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

(OP)
Root functions seems to work for this couse I can get numeric value.
Anyother ideas?

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

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

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
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

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

(OP)
Sorry I dont understand you
Something on "root" function?

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

No, I think he means -->solve,x and it doesn't work.
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.

(OP)
Thanx

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

Hi guys.
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

#### Quote (mar2805)

I always get warning message saying "divide by zero" sad
What am I doing wrong?
You tell Mathcad to search for a solution in the range from 0 to h.
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

I typed integrate(x^2,0,b)=12.5,solve,b and it returned 5 and -5.

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

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

#### Quote (PNachtwey)

I typed integrate(x^2,0,b)=12.5,solve,b and it returned 5 and -5.
Thats one of the possible ways to answer the original question which I posted here 12 days ago. See above.

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

#### Quote:

Quote (PNachtwey)
I typed integrate(x^2,0,b)=12.5,solve,b and it returned 5 and -5.
Just saw it - I hope you didn't really type x^2, otherwise this would mean you have a corrupt copy of mathcad

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

I am having a similar issue in that I use a solve block to solve for two unknowns say C1 & C2. I use the Find(C1,C2) and it gives me the values in a 1x2 Matrix form. After the solve/find block I would like to use C1 and C2 in further equations but they are not defined. I have to manually set C1= to the value I see in the find block. How do I define C1 & C2 as the values in the Find block?

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

Shinerttuâ€¦

You can extract values from vectors and matrices by using array subscripts. For example (and asusming ORIGIN=0), if you have Res:=Find(C1,C2)=[C1 C2], you can get C1 out of the result vector by using Res[0= and you can get C2 by using Res[1=. The "[" keystroke gets you the array subscript. If ORIGIN=1, then use 1 and 2 as 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

Occupant/fel3 thanks!

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!