Question 957416
To draw the net of a cone first draw a straight line and mark a point P (point of cone) Use this as center and draw a circle with radius S (slant height). The sector of this circle you need is given by circumference of base/circumference 
of slant height circle , in this case
{{{Angle=((20cm(pi))/(40cm(pi)))*360degrees}}}=180 degrees.
So draw a half circle with radius 20cm (slant height) and tangent to this half circle(touching edge to edge) draw a complete circle with radius 10cm. This is the base, the larger half circle is the sides, and the net is done.