unexpected result

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2 total messages Started by Bob Kline Wed, 27 Jan 1993 17:10

#1017

Author: Bob Kline
Date: Wed, 27 Jan 1993 17:10

19 lines
953 bytes

	Running mma 2.1 on a Sparc-2, I input the following:

	Solve[{Sqrt[x]+y==11,x+Sqrt[y]==7},{x,y}].



	this results in four roots.  substituting the result in
	Sqrt[x]+y (or Sqrt[y]+x), only two of the roots are
	correct.  the other two are numbers like 14.nnn and 17.nnn.


	if someone has time, please see if your setup has any
	difficulty here.

	thanks.

	-r. kline
	rvk@blink.att.com

Re: unexpected result

#1029

Author: Arthur Rubin
Date: Wed, 27 Jan 1993 23:04

27 lines
1381 bytes

In <rvk.728154627@wink> rvk@blink.att.com (Bob Kline) writes:


>	Running mma 2.1 on a Sparc-2, I input the following:

>	Solve[{Sqrt[x]+y==11,x+Sqrt[y]==7},{x,y}].



>	this results in four roots.  substituting the result in
>	Sqrt[x]+y (or Sqrt[y]+x), only two of the roots are
>	correct.  the other two are numbers like 14.nnn and 17.nnn.


Try setting the option VerifySolutions-> True.

By default, mma solves the equations:

{u^2 ==x,u+y==11,v^2==y,x+v==7}

and eliminates u and v.  For the remaining solutions, u and/or v is
negative.
--
Arthur L. Rubin: a_rubin@dsg4.dse.beckman.com (work) Beckman Instruments/Brea
216-5888@mcimail.com 70707.453@compuserve.com arthur@pnet01.cts.com (personal)
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