Parabola
By Gloria Grazioli
definition
A perfect parabola is a curve where the distance between a fixed point and another fixed line is the same at all points on the curve. The fixed point is called the focus and the fixed line is called the directrix.
How to graph a parabola
The graph of a quadratica equation with the form
y=ax
2+bx+c
is a parabola.
If a>0 graph of y=ax
2+bx+c forms a parabola that is
concave up
How to graph a parabola
The graph of a quadratica equation with the form y=ax
2+bx+c
is a parabola.
If a<0 graph of y=ax
2+bx+c forms a parabola that is
concave down
How to determine vertex
In order to determine the location of focus and directrix of the parabola, one needs to follow the following steps:
First the given equation of parabola is to be converted in the standard form of parabola
y=ax2+bx+c Find the vertex of the given parabola
𝑉(− 𝑏
2𝑎 ; − 𝑏2 − 4𝑎𝑐
4𝑎 )
How to determine focus and directrix
Find the focus of the given parabola 𝐹(− 𝑏
2𝑎 ; − 𝑏2 − 4𝑎𝑐 − 1
4𝑎 )
Find the directrix of the given parabola
𝑦 = − 𝑏2 − 4𝑎𝑐 + 1 4𝑎
Sketching Parabola
1. Find the vertex
2. Find the intercept (0;f(0))
3. Solve f(x)=0 to find the x coordinates of the x-intercepts (if they exixt)
4. Make sure that you’ve got at least one point to either side of the vertex (you can use the y-intercept and the axis of symmetry to get the second point)
5. Sketch the graph