How do I determine the radius and centre of the following? Round to the nearest tenth. a. [math] x^2+y^2=81[/math]        b. [math] x^2+y^2=1[/math]
The normal drawn to the ellipse (x^2/a^2) + (y^2/b^2) at the extremity of the latus rectum passes through the extremity of the minor axis. What is the eccentricity of this ellipse equal to?