• Nov 1st 2008, 01:25 PM
erinwithane
Hello Everybody

Im not in high School, but I am studying for my GMAT and need some help with some stuff that I havnt done in years.

First

What are the formulas for finding the intercepts of a quadratic equation.

I think negetive b plus minus the square root of 4ac divided by 2a is this correct? which intercept does this give you? Whats the formula for finding the other intercept?

How do you solve a problem where you are given the intercepts and asked to choose which equation?

For example:

What equation has te intercepts of (-1,-5)

No graphing calculators allowed or else this would be easy.
• Nov 1st 2008, 01:38 PM
mr fantastic
Quote:

Originally Posted by erinwithane
Hello Everybody

Im not in high School, but I am studying for my GMAT and need some help with some stuff that I havnt done in years.

First

What are the formulas for finding the intercepts of a quadratic equation.

I think negetive b plus minus the square root of 4ac divided by 2a is this correct? which intercept does this give you? Whats the formula for finding the other intercept?

How do you solve a problem where you are given the intercepts and asked to choose which equation?

For example:

What equation has te intercepts of (-1,-5) Mr F says: If you mean the equation of a graph that passes through the point (-1, -5) then there are an infinite number of possible answers. eg. any line of the form y + 1 = m(x + 5) where m is the (non-zero) gradient of the line.

No graphing calculators allowed or else this would be easy.

The solution to $ax^2 + bx + c = 0$ is $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$.

I strongly advise that you get a hold of a textbook that covers the material in the GMAT.
• Nov 1st 2008, 01:43 PM
erinwithane
isnt there another equation to find Y? I specifically remember there being one, but I cant remember what it is. i had an Algebra Teacher is 8th grade tell me what it was but I cant remember it, and I cant find it online anywhere.

I have a GMAT Study guide but it doesnt do a great job of explaining this stuff.
• Nov 1st 2008, 01:48 PM
mr fantastic
Quote:

Originally Posted by erinwithane
isnt there another equation to find Y? I specifically remember there being one, but I cant remember what it is. i had an Algebra Teacher is 8th grade tell me what it was but I cant remember it, and I cant find it online anywhere.
[snip]

Perhpas if you posted the exact question a more specific answer could be given.

Quote:

Originally Posted by erinwithane
[snip]
I have a GMAT Study guide but it doesnt do a great job of explaining this stuff.

Then get a hold of another book. Library might be a good place to start looking.
• Nov 1st 2008, 01:52 PM
erinwithane
The specific question is what is the formula for finding the Y intercept.
• Nov 1st 2008, 02:01 PM
mr fantastic
Quote:

Originally Posted by erinwithane
The specific question is what is the formula for finding the Y intercept.

If you dont know, maybe somebody else does.

I'm not a mind reader. If you cannot ask a clear question you will not get a clear answer.

To find the y-intercept you substitute x = 0 and solve for y. Do find the x-intercept you substitute y = 0 and solve for x.

Take my advice and get a textbook.

By the way, if you spent a small amount of time looking through these forums you would quickly realise why I find your remark
• Nov 1st 2008, 02:02 PM
erinwithane
Mr F stated

$

img.top {vertical-align:15%;} $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
$
" alt="

$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
$
" />

This is the formula for X.

My question is what is the formula for Y?
• Nov 1st 2008, 02:08 PM
mr fantastic
Quote:

Originally Posted by erinwithane
Mr F stated

$

img.top {vertical-align:15%;} $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
$
" alt="

$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
$
" />

This is the formula for X.

My question is what is the formula for Y?

If $y = ax^2 + bx + c$ then the y-intercept is (0, c). However, if the parabola is not written in standard form then this formula is useless (as are most formulas if you don't understand where they come from).

In general to get the y-intercept you have to substitute x = 0 and solve for y.

Next time try being clearer in what you want to know. It will save a lot of time.