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ptc-29232221-Visitor
1-Visitor
October 8, 2012
Question

quadratic equation

  • October 8, 2012
  • 4 replies
  • 10941 views

MathCAD+Quadratic+equation.JPG

I am trying to put my calculations for concrete footings into MathCAD and can't get this to cooperate. With numbers, it looks like this . . .

MathCAD+Quadratic+equation+numbers.JPG

The answer is approximately 13.08, but I can't seem to figure out how to set it up in MathCAD 14 to automate the calculation. Any insight/help would be appreciated. I tried to work through the help section, but I can't get this one to cooperate.

4 replies

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
October 8, 2012

Send pleace the Mathcad-file!

P
ptc-29232221-VisitorAuthor
1-Visitor
October 8, 2012

Valery,

I don't have a file for this, just trying to work through some of the calculations and get them in MathCAD so I don't have to manually input them.

A
AlanStevens19-Tanzanite
19-Tanzanite
October 8, 2012

Use the Boolean equals.

Quadratic.PNG

Alan

R
RichardJ19-Tanzanite
19-Tanzanite
October 8, 2012

There are many ways to do this in Mathcad. Alan shows one, using the symbolic solver. Another way is to solve numerically using the root function.

root.jpg

P
ptc-29232221-VisitorAuthor
1-Visitor
October 8, 2012

Thanks Richard and please forgive my ignorance as it has been 30+ years since I sat in an algebra class, but I am going to take a shot at what I think is going on here . . .

Is the " - x" at the end of the function is to set the equation equal to zero? and the "root(f(x),x,1,20)" is requesting that MathCAD find the roots of x in the defined function "x" , totally guessing now, but is the "1,20" telling it to go through 20 iterations?

I feel the power, but I am just not one to push the "I believe" button without having a firm understanding of what is going on . . . . Thanks again for your input and help. Others feel free to correct me if I have strayed from the right path

R
RichardJ19-Tanzanite
19-Tanzanite
October 8, 2012

Is the " - x" at the end of the function is to set the equation equal to zero?

Correct.

"root(f(x),x,1,20)" is requesting that MathCAD find the roots of x in the defined function "x" ,

If you mean the root of the function f(x), yes. I.e. it finds the value of x that makes f(x) equal to zero.

totally guessing now, but is the "1,20" telling it to go through 20 iterations?

It finds the root within the range x=1 to x=20. You could of course use other numbers, as long as they emcompass 13.08.

P
ptc-29232221-VisitorAuthor
1-Visitor
October 8, 2012

Thanks Alan, that got me to a correct answer, but . . . can it be done using the variables so that I don't have to manually plug and chug numbers?

MathCAD+Quadratic+equation+numbers.JPG

I tried using this process with the variables and it solved for something, but it got ugly . . .

MathCAD+Quadratic+equation+variables+1.JPG

I removed the " *psi" from the f'c in the denominator to see if that would help, but to no avail . . .

R
RichardJ19-Tanzanite
19-Tanzanite
October 8, 2012

The symbolic solver does not understand units. If you are using units use the root function, which solves numerically.

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