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ps - quadratic root q

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by ccassel » Mon Apr 18, 2011 5:54 pm
How would you explain the answer to this question?

If one root of the equation 2x^2+3x-k=0 is 6, what is the value of k?

A. 90
B. 42
C. 18
D. 10
E. -10

Answer is A
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by vineeshp » Mon Apr 18, 2011 6:04 pm
If 6 is the root of the equation with variable x, it means x can take the value 6.

That is,
2x^2+3x-k=0
Substituting 6 for x,

2*6^2+3*6-k=0

72 + 18 -k =0

k =90
Vineesh,
Just telling you what I know and think. I am not the expert. :)
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by Anurag@Gurome » Mon Apr 18, 2011 7:52 pm
ccassel wrote:How would you explain the answer to this question?

If one root of the equation 2x^2+3x-k=0 is 6, what is the value of k?

A. 90
B. 42
C. 18
D. 10
E. -10

Answer is A
Since one of the roots is 6, so it will satisfy the given quadratic equation, 2x² + 3x - k = 0
So, 2(6)² + 3(6) - k = 0 implies 90 - k = 0 or k = 90

The correct answer is A.
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by manpsingh87 » Mon Apr 18, 2011 10:13 pm
ccassel wrote:How would you explain the answer to this question?

If one root of the equation 2x^2+3x-k=0 is 6, what is the value of k?

A. 90
B. 42
C. 18
D. 10
E. -10

Answer is A
f(x)=2x^2+3x-k; now if 6 is a factor of f(x) than f(x)=0; at x=6..!!!
therefore we have 2*36+28-k=0; k=90..!!
O Excellence... my search for you is on... you can be far.. but not beyond my reach!
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