Simple equation - result far too complex and wrong

[MC_User]

Whats wrong with Mathcad or with that simple equation - why is Mathcad not able to find the two solutions 0 and 3 ??

Needless to say that the given "solution" 3.34 is wrong!

If variable x is restricted to be a positive (or zero) real number the "solution" is shown:

Is this a bug?

I am using Mathcad 14 (M030).

Is Mathcad 15 doing better on the job?

[ValeryOchkov]

Mathcad 15 (MuPAD not Maple - in Maple I have two roots 0 and 3)

[AlanStevens]

Square both sides and Mathcad immediately finds the two solutions:

Alan

[ValeryOchkov]

AlanStevens wrote:

Square both sides and Mathcad immediately finds the two solutions:

Alan

The equation x=0 has one root

The equation x^2=0 has two roots

[ValeryOchkov]

Maple is Maple:

[VladimirN]

MC_User wrote:

...Is Mathcad 15 doing better on the job?

In Mathcad 15 M010 obtained the same result as shown in your screenshot.

[Guest2]

Is this a bug?

Sure, and an interesting one, indeed.

Does anybody know, which symbolic engine ist behind Mathcad Prime 2.0? Is it still MuPad or is it something else?

[MikeArmstrong]

Yes it is MuPad.

Mike

[VladimirN]

Guest2 wrote:

...Does anybody know, which symbolic engine ist behind Mathcad Prime 2.0? Is it still MuPad or is it something else?

No. It still MuPad.

[PhilipOakley]

The value of x can be complex (i.e. have an imaginary part), and each of the three square root terms can be positive or negative in the general case, so that give 4 different potential pairings (after dividing through an common minus sign).

MuPad is of German origin and takes a precise approach to problem solving so does consider all those factors. Maple embeds some common solutions as a short cut, which are actually wrong (incomplete) in the general case.

It is usually necessary to add the unstated assumptions of being real, and positive square root (which is hard) to get the simple answer you are expecting.

[RichardJ]

The answer 3.34 is still wrong though.

[PhilipOakley]

Richard Jackson wrote:

The answer 3.34 is still wrong though.

It's near enough for pit work though (phrase learnt when working in the Durham coalfields;-)

[Guest2]

Richard Jackson wrote:

The answer 3.34 is still wrong though.

Yes, and as a symbolic solution one should no accept approximations. the exact expression which simplyfies to 3.34 is shown partially in a screenshot in the original posting and I can duplicate it here - teriffic.

Wonder what algorithm MuPad is using so it lands a an third order equation.