In the Real Numbers, you follow something like this stream of logic.
x^4 is positive
8 is positive
1 is positive
Negative sign - The right hand side is negative. It cannot be positive. It cannot be zero.
y^2 is positive
How many positive numbers can you name that are equal to a negative number?
Note: When did 2 get to be the square root of 8? Cube root, perhaps.