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HELP Quadratic formula NOOOOOOOO

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Source: — Problem Solving |
Junior | Next Rank: 30 Posts
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Location: Toronto

by dimonya » Tue Feb 03, 2009 9:16 pm
There are two methods for solving these

1. completing the square

2. Using formula (-b+-sqrt(b-4ac))/2a
i prefer to use 2

so first thing is ti het the equation on standard form (ax^2+bx+c=0)

in your case 4x^2-9x=0

where
a=4
b=9
c=0

answers follows
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by Ian Stewart » Wed Feb 04, 2009 5:16 am
dimonya wrote:There are two methods for solving these

1. completing the square

2. Using formula (-b+-sqrt(b-4ac))/2a
i prefer to use 2
Don't forget that it's b^2 - 4ac under the root, not b - 4ac. Fortunately we don't need to use the quadratic formula on the GMAT, as long as we know how to factor. So, if you need to solve for x in the question above:

4x^2 = 9x
4x^2 - 9x = 0
x(4x - 9) = 0

The product of two things is zero --> one of them must be zero:

x = 0
or
4x - 9 = 0 ---> x = 9/4
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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