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in the single variable ''x''. The [[graph of a function|graph]] of a univariate quadratic function is a [[parabola]], a [[curve]] that has an [[axis of symmetry]] parallel to the {{math|''y''}}-axis.
If
The bivariate case in terms of variables ''x'' and ''y'' has the form
with at least one of ''a, b, c'' not equal to zero
▲:<math> f(x,y) = a x^2 + by^2 + cx y+ d x+ ey + f \,\!</math>
▲with at least one of ''a, b, c'' not equal to zero, and an equation setting this function equal to zero gives rise to a [[conic section]] (a [[circle]] or other [[ellipse]], a [[parabola]], or a [[hyperbola]]).
A quadratic function in three variables ''x'', ''y,'' and ''z'' contains exclusively terms ''x''<sup>2</sup>, ''y''<sup>2</sup>, ''z''<sup>2</sup>, ''xy'', ''xz'', ''yz'', ''x'', ''y'', ''z'', and a constant:
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