An astronomer told his granddaughter how she could draw an ellipse by sticking two pins in a sheet of paper both equidistant from and in line with the central point, placing a loop of string around them, and then by putting a pencil in the loop and keeping it tight, go right round. The pencil would thus draw the ellipse, each pin being at a focus.

He then asked her to draw the biggest ellipse she could on a sheet of paper 50 centimetres long and 30 cm wide, and then to find the area of the rectangle she could inscribe in her ellipse whose longest side was equal in length to that of the shorter side of the original sheet.

How far apart must she place the pins? How long was the string? What was the area of the inscribed rectangle?

Note: Adapted from Enigma # 1733, which appeared in New Scientist on 23 January, 2013.

(In reply to Partial Solution - first and second questions by Kenny M)

The last part is to find the intersection of x=15 with the ellipse so the width is 30.  It's a simple quadratic that yields y=+/- 12.

Posted by Jer on 2023-10-10 15:15:43