Hi.

 

For any right angled triangle the circumcenter is always the midpoint of the hypotynuse.This way the radius of the circumcircle becomes 1/2*length of hypotynuse.Let it be R

 

R = 1/2root(a²+b²)

 

Similarly for incircle we have the relation (let it be r)

r = Area of triangle/Semi-Perimeter

r = ab/a+b+root(a²+b²)

 

Now you can find D+d