English: Here we have points on two circles, connected with straight lines. Rotating the lower circle, we get hyperboloid of one sheet and then a cone. t is the angle by which we rotate the lower circle. Such models can be seen in some museums. Equations are: ${\displaystyle x^{2}+y^{2}=1+(z^{2}-1)\sin ^{2}{t \over 2},t=0..2\pi \,}$