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Quadratic data sufficiency.

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by govind_raj_76 » Sun Jul 18, 2010 8:17 am
What is the solution of the quadratic expression x^2 + bx + 16 ?

A) the two roots are equal.

B) b is odd.

Please explain how to solve this data sufficiency problem ?
Govind
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by aloneontheedge » Sun Jul 18, 2010 9:28 am
govind_raj_76 wrote:What is the solution of the quadratic expression x^2 + bx + 16 ?

A) the two roots are equal.

B) b is odd.

Please explain how to solve this data sufficiency problem ?
IMO E:
stmtn 1 : If roots are equal b will have 2 values + or - 16
stmnt 2: If B is odd roots will be irrational
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by Stuart@KaplanGMAT » Sun Jul 18, 2010 1:09 pm
govind_raj_76 wrote:What is the solution of the quadratic expression x^2 + bx + 16 ?

A) the two roots are equal.

B) b is odd.

Please explain how to solve this data sufficiency problem ?
Hi,

there are two reasons why this is an invalid question - what's the source?

The first problem is that an expression doesn't have a "solution" - you can only solve an equation or inequality.

The second problem is that, even if we change the expression to the equation:

x^2 + bx + 16 = 0,

the two statements are contradictory - something that never happens on the actual GMAT.

If (1) is true, then x must be +4 or -4. If (2) is true, then x can be neither of those values, leaving us with no possible value for x. On the GMAT, there is always at least one value that satisfies both statements.
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by Stuart@KaplanGMAT » Sun Jul 18, 2010 1:12 pm
aloneontheedge wrote:
govind_raj_76 wrote:What is the solution of the quadratic expression x^2 + bx + 16 ?

A) the two roots are equal.

B) b is odd.

Please explain how to solve this data sufficiency problem ?
IMO E:
stmtn 1 : If roots are equal b will have 2 values + or - 16
stmnt 2: If B is odd roots will be irrational
I've already explained why this question isn't valid, but I just want to point out that if B is odd, assuming that we're solving for:

x^2 + bx + 16 = 0,

there are some integer solutions for x.

x^2 + 17x + 16 = 0; x = -16 or -1

x^2 - 17x + 16 = 0; x = 16 or 1
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by aloneontheedge » Sun Jul 18, 2010 7:09 pm
Stuart Kovinsky wrote:
govind_raj_76 wrote:What is the solution of the quadratic expression x^2 + bx + 16 ?

A) the two roots are equal.

B) b is odd.

Please explain how to solve this data sufficiency problem ?
Hi,

there are two reasons why this is an invalid question - what's the source?

The first problem is that an expression doesn't have a "solution" - you can only solve an equation or inequality.

The second problem is that, even if we change the expression to the equation:

x^2 + bx + 16 = 0,

the two statements are contradictory - something that never happens on the actual GMAT.

If (1) is true, then x must be +4 or -4. If (2) is true, then x can be neither of those values, leaving us with no possible value for x. On the GMAT, there is always at least one value that satisfies both statements.
Stuart,
If roots are equal discrimant wil be equal to zero.
using that we get b as +16 r - 16

Stmnt 2: i just plugged odd numbers and found them to be irrational
So chose E
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by Stuart@KaplanGMAT » Mon Jul 19, 2010 1:58 pm
aloneontheedge wrote: If roots are equal discrimant wil be equal to zero.
using that we get b as +16 r - 16

Stmnt 2: i just plugged odd numbers and found them to be irrational
So chose E
Hi,

quadratic expressions don't have roots; only quadratic equations do - that's the primary reason why the question is invalid.

The secondary reason is that, as I outlined in my first post, the two statements have no common answers, something that will never happen on the GMAT.
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by aloneontheedge » Mon Jul 19, 2010 7:36 pm
Stuart Kovinsky wrote:
aloneontheedge wrote: If roots are equal discrimant wil be equal to zero.
using that we get b as +16 r - 16

Stmnt 2: i just plugged odd numbers and found them to be irrational
So chose E
Hi,

quadratic expressions don't have roots; only quadratic equations do - that's the primary reason why the question is invalid.

The secondary reason is that, as I outlined in my first post, the two statements have no common answers, something that will never happen on the GMAT.
Thanks stuart....i guess i just overlooked
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