Directrix
d = 1.81
d = 1.81
点击F or P or D并拖动移动图像。
函数是数学中的一种对应关系，是从非空数集A到实数集B的对应。简单地说，甲随着乙变，甲就是乙的函数。精确地说，设X是一个非空集合，Y是非空数集 ，f是个对应法则 ， 若对X中的每个x，按对应法则f，使Y中存在唯一的一个元素y与之对应 ， 就称对应法则f是X上的一个函数，记作y＝f（x），称X为函数f（x）的定义域，集合{y|y=f（x），x∈R}为其值域（值域是Y的子集），x叫做自变量，y叫做因变量，习惯上也说y是x的函数。对应法则和定义域是函数的两个要素。
You can move the graph up-down, left-right if you hold down the "Shift" key and then drag the graph.
The parabola is defined as the locus of a point which moves so that it is always the same distance from a fixed point (called the focus) and a given line (called the directrix).
The focus of the parabola is at (0,p).
The directrix is the line y=−p.
The focal distance is |p| (Distance from the origin to the focus, and from the origin to the directrix. We take absolute value because distance is positive.)
The point (x, y) represents any point on the curve.
The distanced from any point (x, y) to the focus (0,p) is the same as the distance from (x, y) to the directrix.
