Why is {x:x is an equilateral triangle in a plane} subset of {x:x is a triangle in a same plane} ?
In this case, the universal set given to us is, U = {x:x is a triangle in a same plane}
and set E = {x:x is an equilateral triangle in a plane}.
E is subset of U because U is a set which contains all different types of triangles in it and set E is only the collection of equilateral triangles out of it. So, E is subset of U.
and set E = {x:x is an equilateral triangle in a plane}.
E is subset of U because U is a set which contains all different types of triangles in it and set E is only the collection of equilateral triangles out of it. So, E is subset of U.