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[solved Problem] Weird Things Come Out When Solve This Equation


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#1 EigenCake

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Posted 19 September 2011 - 06:43 AM

On my classpad330, I type:
solve(b+b^2-a^2-a+a*b^2-b*a^2 = 0,a)

This yields a rather complicated solution for a, and the solution is not right!

After playing around, the problem is finally solved by replacing all the "a" in the expression with variable "a" which is appeared on the panel named "2D". Hence,

solve(b+b^2-a^2-a+a*b^2-b*a^2 = 0,a)
This yields the correct solution: a=-1, a=b. :)

#2 Tchrisn

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Posted 10 April 2012 - 12:21 AM

On my classpad330, I type:
solve(b+b^2-a^2-a+a*b^2-b*a^2 = 0,a)

This yields a rather complicated solution for a, and the solution is not right!

After playing around, the problem is finally solved by replacing all the "a" in the expression with variable "a" which is appeared on the panel named "2D". Hence,

solve(b+b^2-a^2-a+a*b^2-b*a^2 = 0,a)
This yields the correct solution: a=-1, a=b. :)


I tried both and get
a=-1,
a=10.
No difference between using an a from Keyboard/abc or VAR. Am using OS 3.06

#3 MicroPro

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Posted 10 April 2012 - 07:21 AM

Hello and welcome Tchrisn, introduce yourself here if you wish.

EigenCake's post was rather old, but I see many people still have problems with these problems.

The difference between letters from the alphabetical keyboard and VAR keyboard is that every letter of the VAR keyboard donates a single variable. For example ab typed from the VAR keyboard means a×b, but ab typed from the alphabetical keyboard shows one variable with the name ab. If you use the alphabetical keyboard to type variables you should put the multiplication signs manually to make sure two variables is not misinterpreted as a single variable (e.g ab^2 should be written as a*b^2).

Since EigenCake's equation doesn't have any multi-letter variable names, his problem was probably another thing: variable `b` may have been previously defined. In this case using "Clear All Variables" from the "Edit" menu should have solved his problem.




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