In classical geometry why is a line considered to be parallel to itself?
95642
What is a parallel line?
25854
$\mathbb{R}^3$ \ $\mathbb{Q}^3$ is union of disjoint lines. The lines are not in an axis diretion.
66539
Why is the determinant the volume of a parallelepiped in any dimensions?
18564
Why is the symmetry variation $\delta_s q$ different from the ordinary variation $\delta q$?
21603
Why is surface tension parallel to the interface?
121014
Why does a vertical line have a SLOPE (steepness) of undefined?
91031
Why is electric field lines away from (+) and toward (-)?
90570
Why are quadrants defined the way they are?
23851
Is there a set of lines in $\mathbb{R}^3$ such that their union is equal to the set of points with not all coordinates rational?
158009
Why is it always the case that, given an equivalence relation R on a set X and a $x \in X$, that x is equivalent to itself?
28701
Why solid angle of a closed surface from exterior is zero?
152494
How is  $Ax + By = C$ the equation of a straight line?
30507
What is the intuitive meaning of line integral with respect to x?
42088
Is there a rigorous definition of a line?
97056
Why is a geometric progression called so?
114437
Why is this the basis for the indiscrete topology?
74665
Must perpendicular (resp. orthogonal) lines meet?