Write an equation for a parabola given vertex and y intercept

Most "text book" math is the wrong way round - it gives you the function first and asks you to plug values into that function. It is negative 8 over negative 4, which is equal to 2, which is the exact same thing we got by reasoning it out.

This is the same thing as 2yb minus 2yk, which is the same thing, actually let me just write that down. I wanted to show you the intuition why this formula even exists.

It is x minus 2 squared. They are frequently used in physicsengineeringand many other areas. I would like to know how to find the equation of a quadratic function from its graph, including when it does not cut the x-axis.

We also saw a graph in the section where we introduced intercepts where an intercept just touched the axis without actually crossing it. So the simplest thing to start here, is let's just square both sides, so we get rid of the radicals.

Now I told you this is the slow and intuitive way to do the problem. This reflective property is the basis of many practical uses of parabolas. Actually, let's say each of these units are 2. Well, that's just gonna be our change in y. And the maximum point on this downward-opening parabola is when this expression right here is as small as possible.

Here are some of them in green: These things cancel out. So if you square both sides, on the left-hand side, you're gonna get y minus k, squared is equal to x minus a, squared, plus y minus b, squared. Parabolas can open up, down, left, right, or in some other arbitrary direction.

We know that a quadratic equation will be in the form: Now, what I want to do is express the stuff in the parentheses as a sum of a perfect square and then some number over here.

So this is 2, 4, 6, 8, 10, 12, 14, In other words, a parabola will not all of a sudden turn around and start opening up if it has already started opening down.

If I wanted this to be a perfect square, it would be a perfect square if I had a positive 4 over here. And the axis of symmetry is the line that you could reflect the parabola around, and it's symmetric. This quantity right here, x minus 2 squared, if you're squaring anything, this is always going to be a positive quantity.

It's gonna be our change in x, so, x minus a, squared, plus the change in y, y minus b, squared, and the square root of that whole thing, the square root of all of that business. Given a focus at a point a,band a directrix at y equals k, we now know what the formula of the parabola is actually going to be.

And when you multiply it by negative 2, it's going to become negative and it's going to subtract from You can calculate the values of h and k from the equations below: If the parabola opens downward like this, the vertex is the topmost point right like that.

Vertex method Another way of going about this is to observe the vertex the "pointy end" of the parabola. So, let's divide everything, two times, b minus k, so, two times, b minus k.

Well let's get the k squared on this side, so let's subtract k squared from both sides, so, subtract k squared from both sides, so that's gonna get rid of it on the left-hand side, and now let's add 2yb to both sides, so we have all the y's on the left-hand side, so, plus 2yb, that's gonna give us a 2yb on the left-hand side, plus 2yb.

We just substitute as before into the vertex form of our quadratic function. All quadratic functions has a U-shaped graph called a parabola. The parent quadratic function is $$y=x^{2}$$ The lowest or the highest point on a parabola is called the vertex. The vertex has the x-coordinate $$x=-\frac{b}{2a}$$ The y-coordinate of the vertex is.

Name: _____ Date _____ Tons of Free Math Worksheets at: © makomamoa.com Write the equation of the axis of symmetry, and find the coordinates of the vertex of the parabola y = − 3 x 2 − 6 x + 4. The equation of the axis of symmetry for the graph of y = a x 2 + b x + c.

A parabola is a graph of a quadratic function, y = x 2, for example. The line perpendicular to the directrix and passing through the focus (that is, the line that splits the parabola through the middle) is called the " axis of symmetry ". Finding the focus of a parabola given its equation If you have the equation of a parabola in vertex form y = a (x − h) 2 + k, then the vertex is at (h, k) and the focus is (h, k + 1 4 a).

Mar 28,  · Write an equation in vertex form of the parabola that has the same shape as the graph of f(x) = 2x2, but with the point (7, 4) as its makomamoa.com: Resolved.

Write an equation for a parabola given vertex and y intercept
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