Short mathematical tutorial that explains you on How to find vertex, focus and directrix of a parabola equation.
What is a Parabola?
A parabola
is a curve where any point is at an equal distance from a fixed point
(called the focus), and a fixed straight line (called the directrix).
There are two form of Parabola Equation Standard Form and Vertex Form.
Standard Form:
y = ax2 + bx + c
Vertex Form:
y = a(x - h)2 + k
The Vertex of the Parabola:
The vertex is a point V(h,k) on the parabola. Where, h and k can be found using the formula,
h = -b / 2a
k = 4ac - b2 / 4a
The Focus of the Parabola:
The focus is the point that lies on the axis of the symmetry on the parabola at,
F(h, k + p),
with p = 1/4a.
The Directrix of the Parabola:
The directrix of the parabola is the horizontal line on the side of the vertex opposite of the focus. The directrix is given by the equation.
y = k - p
This short tutorial helps you learn how to find vertex, focus, and directrix of a parabola equation with an example using the formulas.
Example: Consider a parabolic equation of the standard form y = 3x2 + 12x + 1. Find the vertex, focus and directrix.
Given:
y = 3x2 + 12x + 1
Solution:
We know that, the standard form of parabola equation is,
y = ax2 + bx + c
From which we know,
a = 3
b = 12
c = 1
Step 1: Finding Vertex of the Parabola Equation
Vertex V = (h,k)
Applying the values in the formula, we get,
h = -b / 2a = -12 / 2(3) = -2
k = 4ac - b2 / 4a = 4(3x12)
Vertex V(-2, 0)
Step 2: Finding Focus of the Parabola Equation
F(h, k + p),
with p = 1/4a
Applying the values in the formula, we get,
p = 1 / 4(3) = 0.083
k + p = 0 + 0.083 = 0.083
Focus F(-2, 0.083)
Step 3: Finding Directrix of the Parabola Equation
Applying the values in the formula, we get,
y = k - p = 0 - 0.083 = -0.083
y = -0.083