Can this be solved with any HP CAS?
09-29-2017, 05:57 PM
Post: #21
 Csaba Tizedes Senior Member Posts: 414 Joined: May 2014
RE: Can this be solved with any HP CAS?
(09-29-2017 02:26 AM)SlideRule Wrote:  ...the expression a+b = c+b represents the original equation...

Unfortunately this is not true, because we have no information about 'b' when we substract it from both sides of the equation.

The correct way, as we learned in the school:

In $$\frac{1}{x-5}$$ the $$x-5\neq0$$, therefore $$x\neq5$$, so $$x\in\Bbb R\backslash\{5\}$$

If $$x\neq5$$, $$\frac{1}{x-5}$$ is a number, therefore we can substract both sides of equation and we can solve the equation $$3x=15$$, the solution is $$x=5$$. But $$x\in\Bbb R\backslash\{5\}$$, therefore $$x=5$$ is not a solution.

The right solution of the original equation is "no solution".

The Skynet: If Skynet has a good CAS that will never found $$x=5$$, because that CAS know that $$x\in\Bbb R\backslash\{5\}$$. But the CAS of any HP, TI, Maple, Mathematica, etc... gives the wrong $$x=5$$ - so the world will be destroyed...

Csaba
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