SOLUTION: Hello. Please and I mean Please, help me know how to find the y value in a parabola. The y value should either be the highest or the lowest point in a positive or negative curved

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Question 148665: Hello. Please and I mean Please, help me know how to find the y value in a parabola. The y value should either be the highest or the lowest point in a positive or negative curved u. Thank you very much for your time in helping me solve this question.
Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
Hello. Please and I mean Please, help me know how to find the y value in a parabola. The y value should either be the highest or the lowest point in a positive or negative curved u. Thank you very much for your time in helping me solve this question.

The formula for the vertex of a parabola, which
is the highest or lowest point, whose equation is:

y+=+Ax%5E2%2BBx%2BC

First we calculate the discriminant

D=B%5E2-4AC.

then the vertex is

(-B%2F%282A%29, -D%2F%284A%29) 

Example:

For the parabola 

y+=+-x%5E2%2B2x%2B8

We can find a few points by selecting
arbitrary values for x, substituting
and finding the y-values.

For example, if we substitute x=-1
into

y+=+-x%5E2%2B2x%2B8
y+=+-%28-1%29%5E2%2B2%28-1%29%2B8
y+=+-1-2%2B8
y+=+5

So we have the point (-1,5)

We can find others the same way.

I found (-3,-7), (-1,5), (0,8), (3,5), and (5,-7).

Let's plot those:



We compare this problem:

y+=+-x%5E2%2B2x%2B8

to

y+=+Ax%5E2%2BBx%2BC

and find A=-1, B=2, C=8

To find the vertex, we first calculate the discriminant

D=B%5E2-4AC=%282%29%5E2-4%28-1%29%288%29+=+4%2B32=36.

then the vertex is

(-B%2F%282A%29, -D%2F%284A%29) =

(-%282%29%2F%282%28-1%29%29, -%2836%29%2F%284%28-1%29%29) =

(-2%2F%28-2%29, -%2836%29%2F%28-4%29) =

(1, 9) =

So we plot the vertex at (1, 9)



and sketch in the parabola:



Edwin