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  2. Playfair's axiom - Wikipedia

    en.wikipedia.org/wiki/Playfair's_axiom

    De Morgan’s argument runs as follows: Let X be the set of pairs of distinct lines which meet and Y the set of distinct pairs of lines each of which is parallel to a single common line. If z represents a pair of distinct lines, then the statement, For all z, if z is in X then z is not in Y,

  3. Transversal (geometry) - Wikipedia

    en.wikipedia.org/wiki/Transversal_(geometry)

    Consecutive interior angles are the two pairs of angles that: [4] [2] have distinct vertex points, lie on the same side of the transversal and; are both interior. Two lines are parallel if and only if the two angles of any pair of consecutive interior angles of any transversal are supplementary (sum to 180°).

  4. Arrangement of lines - Wikipedia

    en.wikipedia.org/wiki/Arrangement_of_lines

    For each pair of lines, there can be only one cell where the two lines meet at the bottom vertex, so the number of downward-bounded cells is at most the number of pairs of lines, () /. Adding the unbounded and bounded cells, the total number of cells in an arrangement can be at most n ( n + 1 ) / 2 + 1 {\displaystyle n(n+1)/2+1} . [ 5 ]

  5. Straightedge and compass construction - Wikipedia

    en.wikipedia.org/wiki/Straightedge_and_compass...

    The group of constructible angles is closed under the operation that halves angles (which corresponds to taking square roots in the complex numbers). The only angles of finite order that may be constructed starting with two points are those whose order is either a power of two, or a product of a power of two and a set of distinct Fermat primes ...

  6. Euler angles - Wikipedia

    en.wikipedia.org/wiki/Euler_angles

    The axes of the original frame are denoted as x, y, z and the axes of the rotated frame as X, Y, Z.The geometrical definition (sometimes referred to as static) begins by defining the line of nodes (N) as the intersection of the planes xy and XY (it can also be defined as the common perpendicular to the axes z and Z and then written as the vector product N = z × Z).

  7. Rotation formalisms in three dimensions - Wikipedia

    en.wikipedia.org/wiki/Rotation_formalisms_in...

    Using the x-convention, the 3-1-3 extrinsic Euler angles φ, θ and ψ (around the z-axis, x-axis and again the -axis) can be obtained as follows: = ⁡ (,) = ⁡ = ⁡ (,) Note that atan2( a , b ) is equivalent to arctan ⁠ a / b ⁠ where it also takes into account the quadrant that the point ( b , a ) is in; see atan2 .

  8. Lowest common factor - Wikipedia

    en.wikipedia.org/wiki/Lowest_common_factor

    Lowest common factor may refer to the following mathematical terms: Greatest common divisor, also known as the greatest common factor; Least common multiple;

  9. Quadrilateral - Wikipedia

    en.wikipedia.org/wiki/Quadrilateral

    Isosceles trapezium (UK) or isosceles trapezoid (US): one pair of opposite sides are parallel and the base angles are equal in measure. Alternative definitions are a quadrilateral with an axis of symmetry bisecting one pair of opposite sides, or a trapezoid with diagonals of equal length. Parallelogram: a quadrilateral with two pairs of ...