It is the locus of points such that the sum of their distance from two distinct fixed points is a constant.
It is the locus of a point such that the sum of its distance from two (distinct) fixed points is a constant. So, given two fixed points, F1 and F2, an ellipse is the locus of the point P such that PF1 + PF2 is a constant. That would be an ellipsoid, a 3 dimensional thing. The 2 distances have to be measured in a fixed (2 dimensional) plane.
It is a line segment.
a fixed pulley is a pulley attached to a support.
They are points whose positions do not change under transformations.
one
Infinite lines as for example the diameter of a circle
In Euclidian or plane geometry, there can be only one line through two fixed points. Lines cannot actually be drawn; if you see it it is not a geometric line. If the points are on a curved surface as in a geometry that is non-Euclidian, then there can be infinitely many lines connecting two points.
infinite
It is the locus of points such that the sum of their distance from two distinct fixed points is a constant.
It is the locus of a point such that the sum of its distance from two (distinct) fixed points is a constant. So, given two fixed points, F1 and F2, an ellipse is the locus of the point P such that PF1 + PF2 is a constant. That would be an ellipsoid, a 3 dimensional thing. The 2 distances have to be measured in a fixed (2 dimensional) plane.
A circle is the locus of all points equidistant from a given point, which is the center of the circle, and a circle can be drawn with a compass. (The phrase "locus of points for a circle" does not seem to be conventionally defined.) or true
The fixed points of a function f(x) are the points where f(x)= x.
the set of points equidistant from a fixed point
Physical mixture
A specific mixture has a fixed boiling point.
This set of points forms a circle with the fixed point as its center.