ghgonnet (12/03/82)
This item is likely to come again and again, and we are likely to hear all sort of ridiculous answers again and again. None of the steps are incorrect. The error comes from ignoring that sqrt() is a MULTIVALUED function and that the folk rule of "taking the positive sqrt" DOES NOT ALWAYS WORK. This being an example of such.
ljdickey@watmath.UUCP (09/12/83)
The SQRT function is defined to be non-negative.
Thus the assertion that something negative is "THE square root"
of a number is not the same as saying that the negative number
squares to a number. To be more concrete, we can have
-4 squared is 16
but
-4 is not the suare root of 16.
This is something which confused a famous psychological tester
at the University of Wisconsin who sold his employment screening
quiz to various employers who wanted not to employ dummies.
Unfortunately one of his questions also screened out people with
sound mathematical training.
--
Lee Dickey, University of Waterloo. (ljdickey@watmath.UUCP)
...!allegra!watmath!ljdickey
...!ucbvax/decvax!watmath!ljdickey