Question

medal to correct answer!

Answer 1

o is (0,0)
and
p=(M+N)/2 =1/2 *((0,2b) +(2a,0) ) =1/2 (2a,2b) =(a,b)

so
op = radical ((xo-xp)^2+(yo-yp)^2) distance formula

Answer 2

can you go on ?

Answer 3

op=sqrt{(0-a)^2 +(0-b)^2}