# How to write a function in standard form from a graph

So first I'll do the vertex at 2 comma negative 5, which is right there. This is true when x is equal to 1.

## How to write a function in standard form from a graph

And whose sum is negative 4, which tells you well they both must be negative. This is 20 minus 40 plus Since 0, is on this graph, it will satisfy the equation of the graph. We'll assume the axis of the given parabola is vertical. So this is going to be negative 20 plus 15, which is equal to negative 5. This equation can be solved by factoring. So as I just said, we're going to try to solve the equation 5x squared minus 20x plus 15 is equal to 0. Now the first thing I like to do whenever I see a coefficient out here on the x squared term that's not a 1, is to see if I can divide everything by that term to try to simplify this a little bit. I want to find the places. Or another way of saying it, when does this 5x squared minus 20x plus 15, when does this equal 0? 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? When x equals 2, y is going to be equal to 5 times 2 squared minus 20 times 2 plus 15, which is equal to-- let's see, this is equal to 2 squared is 4. Sometimes it is easy to spot the points where the curve passes through, but often we need to estimate the points. Compare the solutions in 1a with 1b, and take a look at the graph at the right. Negative 3 times negative 1.

Sometimes it is easy to spot the points where the curve passes through, but often we need to estimate the points.

This is my x-axis. Now the first thing I like to do whenever I see a coefficient out here on the x squared term that's not a 1, is to see if I can divide everything by that term to try to simplify this a little bit.

And we got it right. When x equals 2, y is going to be equal to 5 times 2 squared minus 20 times 2 plus 15, which is equal to-- let's see, this is equal to 2 squared is 4.

If we're getting a negative sum here. And if I can graph those three points then I should be all set with graphing this parabola. And whose sum is negative 4, which tells you well they both must be negative. So I'll divide both sides of this equation by 5. If you have the graph of a parabola, can you determine the equation of the function that created the graph?

### Quadratic function in standard form calculator

So this is going to be negative 20 plus 15, which is equal to negative 5. Plus 15 over 5 is 3 is equal to 0 over 5 is just 0. And now we can think about what x's will make this expression 0, and if they make this expression 0, well they're going to make this expression 0. We need to check another point. The fact that their product is positive tells you they both must be positive. Let's see what's possible. But as in the previous case, we have an infinite number of parabolas passing through 1, 0. Since we know that the x-intercepts are integer values, we can read them off the graph to be -3,0 and 4,0.

You can just take three values for x and figure out what the corresponding values for y are and just graph those three points.

Since we know that the x-intercepts are integer values, we can read them off the graph to be -3,0 and 4,0.

### Vertex form to standard form

This equation can be solved by factoring. Our First Equation:. And the other time is at 3 comma 0. And on the right-hand side, we still have that being equal to 0. I want to find the places. We'll assume the axis of the given parabola is vertical. If there are no other "nice" points where we can see the graph passing through, then we would have to use our estimate. Negative 3 times negative 1 is 3. So this is the point 1 comma 0. So I want to figure out those points. Conclusion: Working backward will create an equation, but remember that there are other equations that will also have that same set of solutions.

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