# sqrt() function for complex number in C++

• Last Updated : 17 Aug, 2022

The complex version of sqrt() function is defined in the complex header file. This function is used to calculate the square root of the complex number z with a branch cut along the negative real axis.

Syntax:

```template <class T> complex<T>
sqrt(const complex<T>& z);```

Parameters: This method takes a mandatory parameter z which represents the complex number whose square root is to be calculated.

Return Value: This function returns the square root of the complex number z.

Below program illustrate the sqrt() function for complex number in C++:

## cpp

 `// C++ program to demonstrate``// example of sqrt() function.` `#include ``#include ``#include ` `using` `namespace` `std;` `int` `main()``{``    ``cout << ``"Square root of -9 is "``;``    ``cout << ``sqrt``(complex<``double``>(-9.0, 0.0)) << endl;` `    ``cout << ``"Square root of (-9, -0) is "``;``    ``cout << ``sqrt``(complex<``double``>(-9.0, -0.0)) << endl;` `    ``return` `0;``}`

Output

```Square root of -9 is (0,3)
Square root of (-9, -0) is (0,-3)```

Time Complexity: O(√(a2+b2)) where a and b are the real and imaginary part of complex number.
Auxiliary Space: O(1)

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