if the tangent of two intersecting circles, at their points of intersection are perpendicular, the circles are said to be orthogonal.
Show that the circles x^2+y^2-6x+4y+2=0 and x^2+y^2+8x+2y-22=0 are orthogonal.
find the equation of the tangent to the ellipse x^2/a^2 + y^2/b^2 =1 at the point (a cos theta, b sin theta)
show that the equation of the tangent to the ellipse x^2/a^2 + y^2/b^2 =1 at the point (x1, y1) is xx1/a^2 + yy1/b^2 = 1.