# Write an equation using a graph

What happens if we multiply both numbers by the same value c? I woutould like to know how to find the equation of a quadratic function from its graph, including when it does not cut the x-axis. Modelling This is a good question because it goes to the heart of a lot of "real" math.

## SparkNotes: Graphing Equations: Ordered Pairs

Often we have a set of data points from observations in an experiment, say, but we don't know the function that passes through our data points. Most "text book" math is the wrong way round - it gives you the function first and asks you to plug values into that function.

A quadratic function's graph is a parabola The graph of a quadratic function is a parabola. The parabola can either be in "legs up" or "legs down" orientation.

## How do you write an equation with just a graph? () | Wyzant Resources

We know that a quadratic equation will be in the form: Sometimes it is easy to spot the points where the curve passes through, but often we need to estimate the points.

Let's start with the simplest case. We'll assume the axis of the given parabola is vertical.

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Parabola cuts the graph in 2 places We can see on the graph that the roots of the quadratic are: Now, we can write our function for the quadratic as follows since if we solve the following for 0, we'll get our 2 intersection points: But is this the correct answer?

Here are some of them in green: And don't forget the parabolas in the "legs down" orientation: So how do we find the correct quadratic function for our original question the one in blue?

System of Equations method To find the unique quadratic function for our blue parabola, we need to use 3 points on the curve. We can then form 3 equations in 3 unknowns and solve them to get the required result.

## Other Dice Activities

We'll use that as our 3rd known point. Vertex method Another way of going about this is to observe the vertex the "pointy end" of the parabola. We can write a parabola in "vertex form" as follows: In our example above, we can't really tell where the vertex is.

If there are no other "nice" points where we can see the graph passing through, then we would have to use our estimate. The next example shows how we can use the Vertex Method to find our quadratic function. One point touching the x-axis This parabola touches the x-axis at 1, 0 only.

What is the value of "a"? But as in the previous case, we have an infinite number of parabolas passing through 1, 0. Here are some of them: No points touching the x-axis Here's an example where there is no x-intercept.

We can see the vertex is at -2, 1 and the y-intercept is at 0, 2. We just substitute as before into the vertex form of our quadratic function.Any straight line on an x- and y-coordinate graph can be described using the equation y = mx + b.

## Sciencing Video Vault

The x and y term refer to a specific coordinate point on the graphed line. The equation of a line is typically written as y=mx+b where m is the slope and b is the y-intercept..

If you know two points that a line passes through, this page will show you how to find the equation of the line. A scatter plot features points spread across a graph's axes.

The points do not fall upon a single line, so no single mathematical equation can define all of them. Yet you can create a prediction equation that determines each point's coordinates.

From the collected data from the research, the data was plotted on the graph to get the curve on the graph.

So how do we find the equation of curve from the graph (curve on the graph is similar to. Students will be able to write the equation for a polynomial given a graph of the polynomial, including when x-intercepts in the polynomial have a multiplicity greater than 1. Big Idea Students apply knowledge about x-intercepts, degree and end behavior of polynomials to write equations to match polynomial graphs. Graphing Linear Equations using X/Y Tables Part 1: Tell whether the ordered pair is a solution of the equation.

Just substitute the given x and y to see if the equation “works”. Write “solution” if it works and “not a solution” if it doesn’t. 1) y = 4x + 2; (2, 10).

Determining the Equation of a Line From a Graph Worksheet | Wyzant Resources