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How do I find the equation for a parabola?
How do I find the equation for a parabola using a graph, and with coordinates already plotted.
If it makes any difference, its the parabola that goes from up to down, with the maximum value.
2 Answers
- railbuffLv 71 decade agoFavorite Answer
y = a(x - p)^2 + q
a is the "stretch" - a>0 ==> parabola opens upwards and has a minimum, a < 0 ==> parabola opens downward and has a maximum. Either of these occur at the vertex, which is (p,q).
The axis of symmetry is vertical and passes through the vertex - it's equation is x = p
Graph the vertex: (p,q)
Draw in the axis of symmetry: x = p
Find a point using a value of x other than p. find y
Graph the point (x,y)
Repeat until you are comfortable with the shape of the graph
Connect the dots with a smooth line.
Source(s): retired math teacher - gooberLv 71 decade ago
The general form is y = ax^2 + bx + c
You need to find the values for a b and c
So you will need the coordinates for three points. Plug the x and y values into the general equation and then get an equation in a b and c for each point.
Solve these three equations for a b and c.
