Ellipse with minor axis 80, major axis 120 Use the Concentric Circle Method or Trammel Method: Draw major axis AB = 120mm, minor axis CD = 80mm, intersecting at center O. Draw two circles: radius 60mm and 40mm, same center O. Draw lines from center through both circles. Project horizontally from big circle, vertically from small circle. Where they meet = point on ellipse. Repeat for many points, join with French curve.

You've outlined the Concentric Circle Method perfectly for constructing the ellipse! Here are the steps presented clearly:

3. Construct an ellipse of minor and major axes 120mm and 80mm respectively.

Using the Concentric Circle Method:

• Step 1: Draw two perpendicular lines intersecting at a center point O. Along one line, mark the major axis AB = 120mm (so OA = OB = 60mm). Along the other line, mark the minor axis CD = 80mm (so OC = OD = 40mm).
• Step 2: With O as the center, draw two concentric circles. The larger circle will have a radius equal to the semi-major axis (60mm), and the smaller circle will have a radius equal to the semi-minor axis (40mm).
• Step 3: Draw several radial lines from the center O, passing through both circles. For each radial line, from where it intersects the larger circle, draw a horizontal line. From where the same radial line intersects the smaller circle, draw a vertical line. The intersection of these horizontal and vertical lines gives a point on the ellipse.
• Step 4: Repeat Step 3 for many radial lines (e.g., every 15° or 30°) to obtain a sufficient number of points. Carefully join these points using a French curve or freehand to form the smooth curve of the ellipse.