A line with negative slope passes through the point P(5,2) and intersects the x-axis at the point A and the y-axis at the point B.

a. Find the equation of the line for which the length of the segment AB
is the smallest.
b. Find the equation of the line for which sum of the lengths OA +OB
the smallest.
c. Find the equation of the line for which the area of the triangle OAB
is the smallest.