For some positive real number r, the line x + y = r is tangent to the circle x^2 + y^2 = 2r. Find r.
x^2 + y^2 = 2x + 2y
x^2 + y^2 - 2x - 2y = 0
(x-1)^2 + (y-1)^2 = 2
x = 2 and y = 2, and x = 0, y = 0 works.
So r = 0+0 and 2+2, but it has to be positive, meaning the answer is 4. :))
=^._.^=
