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Offline Paul_Caughlin  
#1 Posted : 09 February 2011 22:07:36(UTC)
Paul_Caughlin

Rank: Newbie

Groups: Registered
Joined: 09/02/2011(UTC)
Posts: 2
Location: Saskatoon, Saskatchewan, Canada

I am a very new user, and I'm having trouble using the solve function to solve for the neutral axis location in a reinforced concrete beam. I can solve the function by hand, but I am trying to put my hand calculations into a nice, easy to read format.

When boiled down, the quadratic equation is solve(c^2+62.54c-63839=0,c)=(solved roots)

The roots of the equation are 223.3 and -285.9 using the quadratic formula. SMath is saying there are no real roots and I disagree. Am I doing somthing wrong?

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Offline maweilian  
#2 Posted : 09 February 2011 22:38:07(UTC)
maweilian


Rank: Advanced Member

Groups: Registered
Joined: 09/01/2010(UTC)
Posts: 102
Man
United States
Location: Oregon, USA

Was thanked: 5 time(s) in 5 post(s)
Paul,

Option 1:

You need to use the solve function that requires 4 arguments. However, at this point, the solve function is not robust enough to solve equations if the range specified by the 3rd and 4th arguments of the solve function is too large. See the screenshot below:



As seen above, it may be necessary to graph the function in order to determine the initial guesses for the 3rd and 4th arguments.

See Solve for more info.

Option 2:

Use the polyroots function,



See Polyroots for more info.

Edited by user 09 February 2011 22:43:04(UTC)  | Reason: Not specified

Will Massie
Mechanical Engineer
Oregon, USA
Offline Paul_Caughlin  
#3 Posted : 10 February 2011 00:15:15(UTC)
Paul_Caughlin

Rank: Newbie

Groups: Registered
Joined: 09/02/2011(UTC)
Posts: 2
Location: Saskatoon, Saskatchewan, Canada

Thank you Will. Much appreciated.
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