[upload: not work ??]
a b c d
[1.0 2.0 3.0 0.]… = averageif((a1:d1); (x>=0))
(Converted to an answer.)
You had the x as a kind of unspecified variable in this recent question of yours, too.
You should either stop to use it, and apply the way to give a criterion I showed you, or, at least, explain precisely for what reason you insist on the x and what it is meant to mean. I read it as “the current element of the range in the first parameter position”. The criterion parameter will assume this implicitly. An implicit = is added if no explicit comparator is given.
Did you mean =AVERAGEIF(A1:D1; “>=0”)?
Please note: A Criterion parameter is of a very specific kind. You have to compose it as a text (string) despite the fact that it is designed to become the comparator followed by the right hand part of a comparison (either an equation or an inequation). Only the bodies of functions having Criterion parameters can handle comparisons this way.