General form of a parabola

In summary, the general form of a parabola with a Directrix of x=p and a Focus of (h,k) is given by the equation x=1/2(h-p)[y^2 - 2yk + h^2 + k^2 - p^2]. The vertex of this parabola is located at ((h+p)/2, k) and its focal length is (h-p)/2. This is consistent with the standard form of a parabola, which can be written as x=1/4p(y-k)^2 + (h+p)/2. Therefore, the given equation is the correct general form of the parabola.
  • #1
you_of_eh
24
0
For a parabola whose Directrix is given by the equation x=p and whose Focus is (h,k).

Is this by any chance the correct general form of the parabola?

x=1/2(h-p) [y^2 - 2yk + h^2+k^2-p^2]
 
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  • #2
you_of_eh said:
For a parabola whose Directrix is given by the equation x=p and whose Focus is (h,k).

Is this by any chance the correct general form of the parabola?

x=1/2(h-p) [y^2 - 2yk + h^2+k^2-p^2]
The vertex of a parabola is halfway between the focus and directrix. Here, that is at ((h+p)/2, k) so the focal length is (h+p)/2- p= (h-p)/2. Since the "standard" parabola, with horizontal axis, is [itex]4d(x- x_0)= (y- y_0)^2[/itex], here that would be [4(h-p)/2](x- (h+p)/2)= (y- k)^2 which can be written as [itex]x= \frac{1}{2(h-p)}(y- k)^2+ \frac{h+p}{2}[/itex]. If you take that "(h+p)/2" inside the parentheses you get exactly what you have. Well done!
 
  • #3
Alright perfect! thanks a lot for your time.
 

1. What is the general form of a parabola?

The general form of a parabola is y = ax^2 + bx + c, where a, b, and c are constants and x is the independent variable.

2. How is the general form of a parabola different from the standard form?

The general form of a parabola allows for any value of a, b, and c, while the standard form is written as y = a(x-h)^2 + k where (h,k) is the vertex of the parabola and a determines the shape and direction of the parabola.

3. How do you graph a parabola using the general form?

To graph a parabola in general form, you can use the following steps:

  1. Find the vertex by using the formula x = -b/2a and substituting it into the equation to find the corresponding y value.
  2. Plot the vertex on the coordinate plane.
  3. Find two additional points on the parabola by plugging in different values for x and solving for y.
  4. Plot these points and draw a smooth curve through them to complete the graph.

4. What is the significance of the constant a in the general form of a parabola?

The constant a in the general form of a parabola determines the direction and shape of the parabola. If a is positive, the parabola opens upwards and if a is negative, the parabola opens downwards. The absolute value of a also determines the width of the parabola, with a larger absolute value resulting in a narrower parabola.

5. How is the general form of a parabola used in real-world applications?

The general form of a parabola is often used in physics to model the trajectory of objects under the influence of gravity. It is also used in engineering and architecture to design structures such as bridges and arches. In business, it can be used to model profit or cost functions. In general, the parabola is a useful tool for understanding and predicting the behavior of quadratic relationships in various fields.

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