the square root of a negative value is called an imaginary or number
Imaginary number An imaginary number[note 1] is a complex number that can be written as a real number multiplied by the imaginary unit i,[note 2] which is defined by its property i2 = −1.[1] The square of an imaginary number bi is −b2. For example, 5i is an imaginary number, and its square is −25. Zero is considered to be both real and imaginary.[2]