N this problem, consider the curve y = f(x) = x2-4x +1.

(a) For any real number a, the formula for f ' (a) =

(b) The equation of the tangent line to the curve y=f(x) at the point P=(a, f(a)) is

(c) There are two tangent lines to the curve y=f(x) with x-intercept 8. The x-coordinates of these two points of tangency (listed left to right) are: