A triangle is formed by the tangents at the point \( (2, 2) \) on the curves \( y^2 = 2x \) and \( x^2 + y^2 = 4x \), and the line \( x + y + 2 = 0 \). If \( r \) is the radius of its circumcircle, then \( r^2 \) is equal to ________.