Circle

Circle C has the equation (x-4)² + (y-8)² =289
The point P (x,y) lies on C.
a) Find, in terms of x and y, the gradient of the tangent of C at P.
b) Hence, or otherwise, find an equation of the tangent to C at the point (21,8).

Circle -- coordinate geometry

A circle passes through the points (2,0) and (8,0) and has the y axis as a tangent. Find the two possible equations.