Is there an inverse function for y = 4? Is there an inverse function for y = x ^ 2 that does not specify the domain? Is the inverse function of a function a function

Is there an inverse function for y = 4? Is there an inverse function for y = x ^ 2 that does not specify the domain? Is the inverse function of a function a function

1. The necessary and sufficient condition for the existence of inverse function is that the domain of definition and the domain of value of function are one-to-one mapping;
So y = 4 has no inverse function
2. Similarly, y = x & # 178; if the domain is not defined, there is no inverse function
Because when x > 0, the inverse function is x = √ y
x