[B]I would like to know how to inscribe a regular septegon and a regular nonegon inside acircle separately.

For any shape where the corners touch the inside of a circle, you need to find the radius. Once you have this, using a pentagon (5 sides) as an example, divide the total number of degrees in a circle by the number of sides (in this case 5) which gives 72°. Draw a line from the centre of the circle directly up (@ 0°), then draw the next line from the centre of the circle to the circumference at 72° and so on until you have 5 lines.
Where the radii meet the circumference draw lines (chords) so they connect these points. Remove the Radii and there you have a perfect pentagon inscribed inside a circle.

Hopefully you can now answer your own question.