# Thread: Need some basic algerbra help

1. ## Need some basic algerbra help

Sorry guys for posting such basic question but I can't find it anywhere.

How fo you recognize a quadratic equation? I know about counting the degree and stuff but is there maybe a test that can be done to test each equation?

Like for example: 7x+4xy-2x+5y Is this a quadratic?

Oh and someone told me that xy=6 is also a quadratic...how is that? Because of degree?

THanks guys
Derg

2. From MathWorld: "A quadratic equation is a second-order polynomial equation in a single variable x, $ax^2+bx+c$, where $a \ne 0$."

I don't see how xy=6 is quadratic.

3. Originally Posted by Dergyll
Sorry guys for posting such basic question but I can't find it anywhere.

How fo you recognize a quadratic equation? I know about counting the degree and stuff but is there maybe a test that can be done to test each equation?

Like for example: 7x+4xy-2x+5y Is this a quadratic?

Oh and someone told me that xy=6 is also a quadratic...how is that? Because of degree?

THanks guys
Derg
I suppose you could call it quadratic if you define quadratic as being a second order equation. But I too had thought it was only a quadratic if it the expression was a polynomial.

-Dan

4. Im thinking it depends on how you count the degrees, I've never fully grasped that idea of degrees though...How do you count degrees?

How about the equation 7x+4xy-2x+5y, is it a quadratic? My teacher specifically said that xy=6 is a quadratic, something about a circle being involved...

Any ideas guys?
Thanks a bunch
Derg

5. Got it

This is how my teacher defined it as : A Equation with a degree of 2 is considered as a quadratic equation, so technically xy=6 can be written as
x^1 time y^1 = 6 and the 1 degree from x and y add to be 2. But what exactly is degrees?

So I guess 7x+4xy-2x+5y is a quadratic according this definition...

Derg

6. When you have a multivariable polynomial the degree is the sum of the exponents.

Also, $xy=7$ is a rotated hyperbola, (second degree curve).

7. Sorry.

So does this mean that xy=6 is a quadratic in definition? When I graphed it on my calculator (by dividing both sides my x and then graphing it) and found that it is 2 curved parabolas rotated, one in quadrant 2 and another in 4.

Thanks for the help!
Derg

8. Originally Posted by Dergyll
Sorry.

So does this mean that xy=6 is a quadratic in definition?
In that sense, yes.

When I graphed it on my calculator (by dividing both sides my x and then graphing it) and found that it is 2 curved parabolas rotated, one in quadrant 2 and another in 4.
It is not a pair of parabolas. It is a single hyperbola.