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 Fog123 #1 Posted : 06 July 2022 22:26:55(UTC) Rank: NewbieGroups: Registered Joined: 06/07/2022(UTC)Posts: 2 Hi, I have an polynomial equation (x^3 specifically) which I want to get the roots for. The roots are there if I plug in values from WolframAlpha (https://www.wolframalpha.com/input?i2d=true&i=-21.2Power%5Bx%2C3%5D%2B19707.8Power%5Bx%2C2%5D%2B6628342.5x-1125000000), I also checked on excel by changing x=? I found a root of x~128 but SMath won't do it. On SMath it says no results even after I removed the unit and everything?I have used 'solve' function, but always get a "no real roots" message (see file attached).Can someone help out? Question.sm (15kb) downloaded 11 time(s).Many thanks in advance!
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 Razonar #2 Posted : 06 July 2022 22:35:10(UTC) Rank: Advanced MemberGroups: Registered Joined: 28/08/2014(UTC)Posts: 1,036Was thanked: 581 time(s) in 374 post(s) Hi. Try solve(f(x),x,0,1500)=1223.Best regardsAlvaro
 overlord #3 Posted : 06 July 2022 23:12:34(UTC) Rank: Advanced MemberGroups: Registered Joined: 23/07/2013(UTC)Posts: 869Was thanked: 327 time(s) in 225 post(s) Try to plot these kind of functions to see what is going on.Your function is equals to zero around 1200.Here is your solution with various solvers.Regards Question_answer.sm (22kb) downloaded 13 time(s).
 Jean Giraud #4 Posted : 07 July 2022 00:49:02(UTC) Rank: GuestGroups: Registered Joined: 04/07/2015(UTC)Posts: 6,263Was thanked: 915 time(s) in 743 post(s) Originally Posted by: Fog123 I have an polynomial equation ... which I want to get the roots for.Your polynomial is doctored in yellow.By inspection, the plot reveals complex roots, i.e: 2 complex roots.Comment: respect preciously the Lagrange canonical order.Cheers ... Jean. Question Doctored.sm (30kb) downloaded 13 time(s).
 overlord #5 Posted : 07 July 2022 03:58:06(UTC) Rank: Advanced MemberGroups: Registered Joined: 23/07/2013(UTC)Posts: 869Was thanked: 327 time(s) in 225 post(s) Here is your complete answer by the way.Good old maple saves the day again.Regards
 Jean Giraud #6 Posted : 07 July 2022 13:59:06(UTC) Rank: GuestGroups: Registered Joined: 04/07/2015(UTC)Posts: 6,263Was thanked: 915 time(s) in 743 post(s) As it looks, if you create cubic at profusion,the cubic roots solver will be a great companion.It comes useful in PID techniques.Polyroots is native in Smath.
 Jean Giraud #7 Posted : 07 July 2022 14:38:23(UTC) Rank: GuestGroups: Registered Joined: 04/07/2015(UTC)Posts: 6,263Was thanked: 915 time(s) in 743 post(s) ... once your cubic in hand, you can solve for a specific datum.Cheers ... Jean.
 Fog123 #8 Posted : 11 July 2022 17:24:19(UTC) Rank: NewbieGroups: Registered Joined: 06/07/2022(UTC)Posts: 2 Hi Everyone,Thank you for your replies they were very helpful. I really appreciate the people who went above and beyond to explain the various ways of getting the roots and even changing the datum. It proved extremely helpful to plot the function where I quickly realized the difference between my SMath and WolframAlpha results. The 4th term 'x4' or 'c' is supposed to be a negative. I though I was doing something wrong with inputting the data into SMath, but it was the function which I was inputting that was wrong. In my program by changing "Qd" to a (negative) I got the following roots.Lesson learned: Quadruple check your functions. Question_finished.sm (22kb) downloaded 6 time(s).
 Jean Giraud #9 Posted : 11 July 2022 19:10:43(UTC) Rank: GuestGroups: Registered Joined: 04/07/2015(UTC)Posts: 6,263Was thanked: 915 time(s) in 743 post(s) Good job ! Start be friend with Lagrange canonic. Question_finished Canonic Lagrange.sm (28kb) downloaded 2 time(s).
 Jean Giraud #10 Posted : 11 July 2022 19:32:16(UTC) Rank: GuestGroups: Registered Joined: 04/07/2015(UTC)Posts: 6,263Was thanked: 915 time(s) in 743 post(s) ... read more in pink.Cheers ... Jean. Question_finished Canonic Lagrange.sm (34kb) downloaded 1 time(s).
 overlord #11 Posted : 11 July 2022 20:05:45(UTC) Rank: Advanced MemberGroups: Registered Joined: 23/07/2013(UTC)Posts: 869Was thanked: 327 time(s) in 225 post(s)
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