Half-plane

In mathematics, the upper half-plane, ⁠${\displaystyle {\mathcal {H}},}$⁠ is the set of points ⁠${\displaystyle (x,y)}$⁠ in the Cartesian plane with ⁠${\displaystyle y>0.}$⁠ The lower half-plane is the set of points ⁠${\displaystyle (x,y)}$⁠ with ⁠${\displaystyle y<0}$⁠ instead. Arbitrarily oriented half-planes can be obtained via a planar rotation. Half-planes are an example of two-dimensional half-space. A half-plane can be split in two quadrants.