Step-by-step explanation:
It falls out from the definition of a square root and the rules of exponents.
If r is a square root of x, then ...
r×r = x
The rules for exponents tell you ...
(a^b)(a^c) = a^(b+c)
So if r is some power (a) of x, then ...
r×r = (x^a)(x^a) = x^(a+a) = x^(2a)
but we have said that r×r = x, so ...
x^(2a) = x = x^1
Equating exponents, we have ...
2a = 1
a = 1/2
So ...
r = x^(1/2) . . . . . the square root of x