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Surd [x,n]

gives the real-valued n^(th) root of x.

Details
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
Numerical Evaluation  
Specific Values  
Visualization  
Show More Show More
Function Properties  
Differentiation  
Integration  
Series Expansions  
Applications  
Properties & Relations  
Possible Issues  
Neat Examples  
See Also
Related Guides
Related Links
History
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Surd [x,n]

gives the real-valued n^(th) root of x.

Details

  • Surd [x,n] returns the real-valued n^(th) root of real-valued x for odd n.
  • Surd [x,n] returns the principal n^(th) root for non-negative real-valued x and even n.
  • For symbolic x in Surd [x,n], x is assumed to be real valued.
  • Surd can be evaluated to arbitrary numerical precision.
  • Surd automatically threads over lists. »
  • In StandardForm , Surd [x,n] formats as .
  • can be entered as surd, and moves between the fields.
  • Surd can be used with Interval and CenteredInterval objects. »

Examples

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Basic Examples  (5)

Surd gives a real-valued root:

Plot over a subset of the reals:

Enter using surd, then use :

Note that this is not the same as , which is Power [x,1/3]:

Compare the real and imaginary parts of and over the reals:

Series expansion:

Scope  (31)

Numerical Evaluation  (5)

Evaluate numerically:

Evaluate to high precision:

The precision of the output tracks the precision of the input:

Evaluate efficiently at high precision:

Compute the elementwise values of an array using automatic threading:

Or compute the matrix Surd function using MatrixFunction :

Compute worst-case guaranteed intervals using Interval and CenteredInterval objects:

Or compute average-case statistical intervals using Around :

Specific Values  (4)

Values at fixed points:

Evaluate symbolically:

Values at infinity:

Find a value of x for which (RadicalBox[x, 2, MultilineFunction -> None, SurdForm -> True])=1.5:

Substitute in the result:

Visualize the result:

Visualization  (4)

Plot the Surd function for various orders:

Visualize the absolute value and argument (sign) of for odd n:

The function has the same absolute value but a different argument for :

Compare the real and imaginary parts of and for even n:

Polar plot with :

Function Properties  (8)

Surd [x,n] is defined for all real x when n is a positive, odd integer:

For positive, even n, it is defined for non-negative x:

For negative n, 0 is removed from the domain:

Surd is not defined for nonreal complex values:

Surd [x,n] achieves all non-negative real values when n is a positive even integer:

For positive odd n, its range is the whole real line:

For negative n, 0 is removed from the range:

Surd [x,n] is not an analytic function of x for any integer n:

is increasing for positive :

Decreasing for negative even :

Indefinite for negative odd :

is injective for :

Visualize for :

And it is surjective onto for odd, positive , but not other values of :

Visualize for :

has indefinite sign for odd :

It is non-negative on its real domain for even :

in general has both singularities and discontinuities at zero:

However, for positive odd it is continuous at the origin:

is neither convex nor concave for odd :

On its domain of definition, it is concave for positive even and convex of negative even :

Differentiation  (3)

The first derivative with respect to x:

Higher derivatives with respect to x:

Plot the higher derivatives with respect to x:

Formula for the ^(th) derivative with respect to x:

Integration  (3)

Compute the indefinite integral using Integrate :

Verify the anti-derivative:

Definite integral:

More integrals:

Series Expansions  (4)

Find the Taylor expansion using Series :

Plots of the first three approximations around :

General term in the series expansion using SeriesCoefficient :

The first-order Fourier series:

The Taylor expansion at a generic point:

Applications  (1)

With , the real vector field corresponding to the complex function is , and the trajectories that follow the field satisfy the differential equation . The implicit solution is for real , which corresponds to a family of circles that are tangent to the real axis at the origin:

In polar coordinates, the trajectories are for any real :

More generally, for where is an integer, the streamlines follow for constant :

This also works for negative powers:

For odd powers, care must be taken to ensure the first argument to Surd is non-negative:

Properties & Relations  (3)

Surd [x,n] is only defined for real x and integer n:

Surd [x,n] is a bijection onto its domain of definition for every nonzero integer n:

Use Surd [x,n] to find the n^(th) real root:

Use Power [x,1/n] or to find the principle complex root:

Possible Issues  (1)

On the negative real axis, Surd [x,n] is undefined for even n:

On the negative real axis, Surd [x,n] is different from the principal root returned by Power [x,1/n]:

Neat Examples  (1)

Plot a composition of Surd :

See Also

Power   Sqrt   CubeRoot   Re

Wolfram Research (2012), Surd, Wolfram Language function, https://reference.wolfram.com/language/ref/Surd.html.

Text

Wolfram Research (2012), Surd, Wolfram Language function, https://reference.wolfram.com/language/ref/Surd.html.

CMS

Wolfram Language. 2012. "Surd." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Surd.html.

APA

Wolfram Language. (2012). Surd. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Surd.html

BibTeX

@misc{reference.wolfram_2025_surd, author="Wolfram Research", title="{Surd}", year="2012", howpublished="\url{https://reference.wolfram.com/language/ref/Surd.html}", note=[Accessed: 10-January-2026]}

BibLaTeX

@online{reference.wolfram_2025_surd, organization={Wolfram Research}, title={Surd}, year={2012}, url={https://reference.wolfram.com/language/ref/Surd.html}, note=[Accessed: 10-January-2026]}

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