Other geometric equations from two dimensions will find familiar analogues in three dimensions. For example, recall the formula for a circle centered at the origin in the plane, <math>x^2 + y^2 = r^2 \ </math>, where <math>r \ </math> is the radius of the circle. It should come as no shock to learn the formula for a sphere in three dimensions is <math>x^2 + y^2 + z^2 = r^2 \ </math>. Other familiar geometric curves from the plane find analogues in three dimensions as well: just as the shape described by <math>y=x^2 \ </math> in the plane is called a '''parabola''', so the surface described by <math>z=x^2 + y^2 \ </math> is called a '''parabaloid'''. At this time, it is not necessary to discuss all of the various surfaces which appear often - the basic forms are below, and the exercises here and in future lectures will be sufficient to introduce the student to them. | Other geometric equations from two dimensions will find familiar analogues in three dimensions. For example, recall the formula for a circle centered at the origin in the plane, <math>x^2 + y^2 = r^2 \ </math>, where <math>r \ </math> is the radius of the circle. It should come as no shock to learn the formula for a sphere in three dimensions is <math>x^2 + y^2 + z^2 = r^2 \ </math>. Other familiar geometric curves from the plane find analogues in three dimensions as well: just as the shape described by <math>y=x^2 \ </math> in the plane is called a '''parabola''', so the surface described by <math>z=x^2 + y^2 \ </math> is called a '''parabaloid'''. At this time, it is not necessary to discuss all of the various surfaces which appear often - the basic forms are below, and the exercises here and in future lectures will be sufficient to introduce the student to them. |