Lisandro is using this diagram to find the equation of a circle. He notices that the radius, the blue line, and the red line form a right triangle. Which shows his correct reasoning and equation

a) The length of the red line is |x + h|.
The length of the blue line is |y + k|.
The equation of a circle is (x + h)2 + (y + k)2 = r2.

b) The length of the radius is r.
The area of a circle is πr2.
The equation of the circle is y = πr2x.

c) The length of the red line is |x – h|.
The length of the blue line is |y – k|.
The equation of a circle is (x – h)2 + (y – k)2 = r2.

d) The length of the red line is |x – h|.
The length of the blue line is |y – k|.
The equation of a circle is (x – h)2 + (y – k)2 = r.