为什么math.Pow10（e int）返回float64而不是int64？

Since parameter e is int, why not just return an int64? Is there any special reason for this?

2 reasons:

First, the parameter may be negative too, in which case the result is a fraction number between 0 and 1, so a float64 return value is not just justified but needed.

fmt.Println(math.Pow10(-1))

Output (try it on the Go Playground):

0.1

Second, almost^* every function of the math package returns value(s) of type float64, adding one that doesn't would break "consistency".

^{[*] Few exceptions include functions like Float32frombits() and llogb() where the deviation is justified.}