To find the y-intercept, simply set the value of x equal to 0, and solve for y, or f(x).
f(x) = 0^2 - 3(0) - 40
f(x) = -40
The y-intercept is -40.
Because this is a 2nd degree polynomial, we cannot find the x-intercepts in one step, and must instead use one of a few different methods.
In this case, we're going to use the quadratic formula:
Plug in the values.
3 +/- √(-3^2 + 160) / 2
3 +/- √169 / 2
3 +/- 13 / 2
(3 + 13) / 2 = 16 / 2 = 8
(3 - 13) = -10 / 2 = -5
The x intercepts are 8, and -5.