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: <math>f^{-1}(y) = \sqrt{y} . </math>
(If we instead restrict to the ___domain {{math| ''x'' ≤ 0}}, then the inverse is the negative of the square root of {{mvar|y}}.)
===Full inverses=== [[File:Inversa d'una cúbica gràfica.png|right|thumb|The inverse of this [[cubic function]] has three branches.]] Alternatively, there is no need to restrict the ___domain if we are content with the inverse being a [[multivalued function]]: : <math>f^{-1}(y) = \pm\sqrt{y} . </math>
Sometimes, this multivalued inverse is called the '''full inverse''' of {{mvar|f}}, and the portions (such as {{sqrt|{{mvar|x}}}} and −{{sqrt|{{mvar|x}}}}) are called ''branches''. The most important branch of a multivalued function (e.g. the positive square root) is called the ''[[principal branch]]'', and its value at {{mvar|y}} is called the ''principal value'' of {{math|''f''<sup> −1</sup>(''y'')}}.
For a continuous function on the real line, one branch is required between each pair of [[minima and maxima|local extrema]]. For example, the inverse of a [[cubic function]] with a local maximum and a local minimum has three branches (see the adjacent picture).
===Trigonometric inverses===
[[Image:Gràfica del arcsinus.png|right|thumb|The [[arcsine]] is a partial inverse of the [[sine]] function.]]
: <math>\sin(x + 2\pi) = \sin(x)</math>
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