The chord of contact from (x1,y1)(x_1, y_1)(x1,y1) to the circle x2+y2=r2x^2 + y^2 = r^2x2+y2=r2 is:
xx1+yy1=r2xx_1 + yy_1 = r^2xx1+yy1=r2
xx1+yy1=0xx_1 + yy_1 = 0xx1+yy1=0
x2+y2=x1x+y1yx^2 + y^2 = x_1x + y_1yx2+y2=x1x+y1y
None of the above