I would just like a second opinion please to ensure I am doing this correctly.

When y = 0

0 = -x^2 + 4x + 5

- 5 = 4x

x = - 1.25

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- September 3rd 2011, 12:46 PMDavid GreenFinding the x- intercept
I would just like a second opinion please to ensure I am doing this correctly.

When y = 0

0 = -x^2 + 4x + 5

- 5 = 4x

x = - 1.25 - September 3rd 2011, 12:51 PMProve ItRe: Finding the x- intercept
- September 3rd 2011, 12:52 PMSironRe: Finding the x- intercept
What happened with the ?

Use the quadratic formula. - September 3rd 2011, 01:03 PMDavid GreenRe: Finding the x- intercept
- September 3rd 2011, 01:05 PMProve ItRe: Finding the x- intercept
- September 3rd 2011, 01:10 PMDavid GreenRe: Finding the x- intercept
- September 3rd 2011, 01:14 PMSironRe: Finding the x- intercept
In the second degree equation:

is that means if we substitute this values in the formula we get:

- September 3rd 2011, 02:25 PMDavid GreenRe: Finding the x- intercept
- September 3rd 2011, 02:28 PMSironRe: Finding the x- intercept
There're two solutions (if ) for a quadratic equation by using the quadratic formula:

So in this case:

- September 3rd 2011, 02:32 PMDavid GreenRe: Finding the x- intercept
- September 3rd 2011, 02:41 PMSironRe: Finding the x- intercept
What do you mean with the 'rest of the formula'? Don't you understand how I got the solutions? ...

- September 3rd 2011, 02:49 PMDavid GreenRe: Finding the x- intercept
I understand the two roots and how you got them, but the formula has been modified.

- b + or - square root D / 2a

See the changes I have not seen before?

Capital D not squared, and - 4ac missing?

Like I said before this subject is new to me and is a new learning curve. - September 3rd 2011, 02:56 PMSironRe: Finding the x- intercept
I don't think the formula has been modified.

In general if you have a quadratic equation:

Then this equation has:

two different solutions (or roots) if

If then the two identical solutions are:

If :

There're no real solutions.

Is this clear? If you need a prove of this then you can ask it. - September 3rd 2011, 02:59 PMDavid GreenRe: Finding the x- intercept
So the capital D, this I now understand to be the solution of;

b^2 - 4ac

then the answer = D which I take the square root value. - September 3rd 2011, 03:03 PMSironRe: Finding the x- intercept
D is the discriminant, and indeed .

I think you get the point now. Do you?