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experts pls help

by Ramit88 » Wed Jan 26, 2011 3:18 am
if (t-8) is a factor of t^2 - kt - 48 , then k = ?

A -6
B -2
C 2
D 6
E 14


ANS C

my ans is coming C
my method
-48 = -6 X -8

whats the mistake m making..?
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by Anurag@Gurome » Wed Jan 26, 2011 3:25 am
Ramit88 wrote:ANS C

my ans is coming C
my method
-48 = -6 X -8

whats the mistake m making..?
Your answer is coming as C and the answer is C too! :)
Only mistake is that is -48 is not equal to (-6)*(-8), it should be (-6)*(8).

Your method is also okay.
Here is another method...

If (t - 8) is a factor of (t² - kt - 48), then (t² - kt - 48) = (t - 8)*(Something)
Hence, if we take t = 8, then the expression must be equal to zero.

Therefore, (8² - 8k - 48) = 0
=> (64 - 8k - 48) = 0
=> 8k = 16
=> k = 2

The correct answer is C.
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by Ramit88 » Wed Jan 26, 2011 3:55 am
Anurag@Gurome wrote:
Ramit88 wrote:ANS C

my ans is coming C
my method
-48 = -6 X -8

whats the mistake m making..?
Your answer is coming as C and the answer is C too! :)
Only mistake is that is -48 is not equal to (-6)*(-8), it should be (-6)*(8).

Your method is also okay.
Here is another method...

If (t - 8) is a factor of (t² - kt - 48), then (t² - kt - 48) = (t - 8)*(Something)
Hence, if we take t = 8, then the expression must be equal to zero.

Therefore, (8² - 8k - 48) = 0
=> (64 - 8k - 48) = 0
=> 8k = 16
=> k = 2

The correct answer is C.

it was a typo anurag.. neways thank u soooooo much :)
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