If f:[0,∞)→f(x)=x2,x∈R then f is
it is a onto function because for every value of y between 0 to infinity there exists a value of x.
for it to be an onto function if there exists one value of x for a unique y then its enough.
in this case we have two values of x for one value of y
example: y=25
x=root(25)=+/−5
∴ given function is onto.