I made a very simple case:

testF[x_, y_, z_] = x^2 + y^2 + z^2
Simplify[testF[x, y, z]]

If {x, y, z} is normalized, the simplified result should just be 1. How could I specify this condition/assumption?

  • 2
    $\begingroup$ Simplify[testF[x, y, z], Assumptions -> x^2 + y^2 + z^2 == 1] works on my end. $\endgroup$
    – user484
    Aug 5, 2013 at 0:36
  • 3
    $\begingroup$ This question appears to be off-topic because it is too localized; i.e, it applies only to local situation and needs of its poster. $\endgroup$
    – m_goldberg
    Aug 5, 2013 at 1:53
  • $\begingroup$ @m_goldberg do you remember why this question was reopened? Because I can't cast a close vote again. $\endgroup$
    – Kuba
    Apr 26, 2014 at 8:07
  • $\begingroup$ @Kuba. No, don't remember. I will write up Narain's comment as community wiki answer. You can up-vote it to get the question off unanswered list. $\endgroup$
    – m_goldberg
    Apr 26, 2014 at 14:45

1 Answer 1


As Rahul Narain wrote in a comment,

testF[x_, y_, z_] = x^2 + y^2 + z^2;
Simplify[testF[x, y, z], Assumptions -> x^2 + y^2 + z^2 == 1]

This may seem trivial, but it precisely expresses the condition for normality.


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