Despite what many high school students believe, you need to know relatively few formulas for the New SAT Math section. The reason why there are so few formulas necessary for SAT Math is that the SAT is meant to test your reasoning skills more than your ability to memorize though in some cases, of course, memorization is necessary. There are always multiple avenues to the solution of a problem, and I teach my students how to take a consistent, accurate approach that utilizes a minimum of formulas and takes the path of least resistance to each answer.

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.

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. 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. 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. 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.But the equation for a parabola can also be written in "vertex form": y = a (x − h) 2 + k In this equation, the vertex of the parabola is the point (h, k).

Use the information provided to write the vertex form equation of each parabola. 1) y = x2 − 4x + 5 2) Vertex Form Practice Use the information provided to write the vertex form equation of each parabola. 1) y = x2 − 4x + 5 y = (x − 2)2 + 1 2) y = x2 − 16 x + The standard form equation for parabolas is one of the two ways to write parabola equations.

Learn what the other one is and how it comes into play when writing standard form equations for parabolas. Just as a quadratic equation can map a parabola, the parabola's points can help write a corresponding quadratic equation.

Parabolas have two equation forms – standard and vertex. In the vertex form, y = a(x - h) 2 + k, the variables h and k are the coordinates of the parabola's vertex.

Write the standard form equation for a vertical or horizontal parabola Calculate the vertex and the focus point of a parabola To unlock this lesson you must be a rutadeltambor.com Member.

The Top 10 SAT Math Formulas You Need to Know for the New SAT and PSAT and the rest of them too. Please note: I am a Harvard grad, SAT/ACT perfect scorer and full-time private tutor in San Diego, California, with 17 years and 17, hours of teaching and tutoring rutadeltambor.com more helpful information, check out my my SAT Action Plan as well as my free e-book, Master the SAT by Brian .

Standard and vertex form of the equation of parabola and how it relates to a parabola's graph.