Answer the following with respect to the concept of surjectivity of functions.
a. Part 1: (i) Define a surjective (onto) function.
b. Part 2: (ii) Let f:R→[0,∞) be given by f(x)=x2. Determine, with justification, whether f is surjective.
c. Part 3: (iii) If the same rule f(x)=x2 is declared with codomain R instead of [0,∞), state with reason whether the function is surjective in this case.