How do you find radius from input circle?

I wrote a code like given below to get a circle equation from user and i need to find radius to make some calculation.(exp :2*x^2 + 2*y^2 = 8)

circle = input('Enter for circular path: ','s') ;

C = str2sym(circle) ;

Answer 1

[Matt J]

syms x y real
syms r real positive

c=2*(x-3)^2 + 2*(y+7)^2 == 8;

c0=str2sym(extractBefore(char(c),'=='));

sol0=solve(c0,[x,y]) %center of circle

sol0 = struct with fields:
    x: 3
    y: -7

c=subs(c,[x,y],[r+sol0.x,sol0.y]);

radius=double( solve(c,r) )

radius = 2