Question

Letters with the diameter of the circle x²+y²=1, where S is the point (1, 0). Let P be a variable point on the circle and tangent.
(a) The equation of the tangent is y=x−1.
(b) The equation of the tangent is y=1−x.
(c) The equation of the tangent is y=x+1.
(d) The equation of the tangent is y=1+x.