In a triangle, the sum of two sides is x and the product of the same two sides is y. If x2−c2=y, where c is the third side of the triangle, then the ratio of the in-radius to the circum-radius of the triangle is
a. \frac{3y}{2x(x+c)}
b. \frac{3y}{2c(x+c)}
c. \frac{3y}{4x(x+c)}
d. \frac{3y}{4c(x+c)}