Draw the graph of function f(x) = x^2.
If the graph is translated down by 4 units the graph is,
The vertex of the function after translation is (0,-4).
The curve intersect the x axis at two points. So zeros are x = 2 and x = -2.
The curve intersect the y axis at y = -4. So y-intercept is -4.
The curve has minimum value and equal minimum value of the translated function is -4.