That means: Find all points on the circle x^2 + y^2 = 81 where the slope OF A LINE DRAWN TANGENT TO THE CIRCLE AT THAT POINT is 9/40.We take the derivative implicitly Divide every term by 2 Substitute 9/40 for (dy)/(dx) Solve for y: Multiply both sides by 40/9 Substitute for y in the equation of the circle: Multiply through by 81 Substituting for x² in the equation of the circle: Multiply through by 1681 So the two points where the slope of the tangent line is 9/40 are: and Edwin