How do you solve a quadratic equation if there are not numbers which multiply to the last number and add to the middle number?
ie:
x^2 - 2x - 8 = 0
or x^2 - 2x - 7 =0
I know that if you have someting like x^2 - 2x - 3 = 0 you can factor it to
x-3 and x+1 but how about the cases above?
thanks!
Quadratic Equation question
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- Brent@GMATPrepNow
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The "official" answer would be to use the quadratic formula, which is far too awful to try to type here. Google "quadratic formula" to learn more.
GMAC includes the quadratic formula in its curriculum but, to date, I have not seen one single official GMAT question that requires the quadratic formula. I do know one instructor who says a former student claims to have had a question that required the quadratic formula, but I'll believe it when I see it. If you ask me, it sounds like an urban myth
The whole quadratic formula thing is a bit of a paradox in that, if you were to see a question requiring this formula, then you are probably scoring in the 750+ range, in which case you probably already know the formula. If you are not scoring in the 750+ range, then you won't see questions requiring the formula so don't waste your time memorizing it. Of course, all of this assumes that there are such questions.
Are there any other GMAT instructors out there who would like to weigh in on this? Am I missing anything?
GMAC includes the quadratic formula in its curriculum but, to date, I have not seen one single official GMAT question that requires the quadratic formula. I do know one instructor who says a former student claims to have had a question that required the quadratic formula, but I'll believe it when I see it. If you ask me, it sounds like an urban myth
The whole quadratic formula thing is a bit of a paradox in that, if you were to see a question requiring this formula, then you are probably scoring in the 750+ range, in which case you probably already know the formula. If you are not scoring in the 750+ range, then you won't see questions requiring the formula so don't waste your time memorizing it. Of course, all of this assumes that there are such questions.
Are there any other GMAT instructors out there who would like to weigh in on this? Am I missing anything?
- logitech
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for examplegxj007 wrote:How do you solve a quadratic equation if there are not numbers which multiply to the last number and add to the middle number?
ie:
x^2 - 2x - 8 = 0
or x^2 - 2x - 7 =0
I know that if you have someting like x^2 - 2x - 3 = 0 you can factor it to
x-3 and x+1 but how about the cases above?
thanks!
x^2 - 2x - 8 = 0
AX^2+BX+C=0
easy method
you have to find the factors of both A and C and try to get B as below:
A = A1xA2
C=C1xC2
And B must be equal to:
B= A1xC2 + A2XC1
lets apply this to:
x^2 - 2x - 8 = 0
1x -4
1x +2
(2x + (-4x) = -2x ( remember B =-2)
so
x^2 - 2x - 8 = 0
(x-4)(x+2)=0
LGTCH
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"DON'T LET ANYONE STEAL YOUR DREAM!"
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"DON'T LET ANYONE STEAL YOUR DREAM!"
GMAT/MBA Expert
- Brent@GMATPrepNow
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Oops, I didn't even notice that the first equation (x^2 - 2x - 8 = 0 ) is factorable.
What about the second equation (x^2 - 2x - 7 =0) ?
Any thoughts about the quadtatic formula?
Do any instructors out there delve deeply into this formula?
I'm quite curious.
What about the second equation (x^2 - 2x - 7 =0) ?
Any thoughts about the quadtatic formula?
Do any instructors out there delve deeply into this formula?
I'm quite curious.
- logitech
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The Quadratic Formula is out of GMAT's scope BUT it does not hurt to learn it..Brent Hanneson wrote:Oops, I didn't even notice that the first equation (x^2 - 2x - 8 = 0 ) is factorable.
What about the second equation (x^2 - 2x - 7 =0) ?
Any thoughts about the quadtatic formula?
Do any instructors out there delve deeply into this formula?
I'm quite curious.
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LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Thanks for your responses. So is it safe to say that the strategy for completing the square is probably out of scope as well? I guess I just want to ensure that I'm not wasting time going too far in depth with certain concepts if they won't even show up on the test.
thanks again!
thanks again!
- logitech
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Old greek saying:gxj007 wrote:Thanks for your responses. So is it safe to say that the strategy for completing the square is probably out of scope as well? I guess I just want to ensure that I'm not wasting time going too far in depth with certain concepts if they won't even show up on the test.
thanks again!
Eat the grape, and don't ask where it s coming from.
Just learn the formula and use it when you need it.
Good luck!
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"