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elizabeth
10-19-2013, 06:57 PM
If x^2-4x>0, then which one of the following could NOT be the value of x ?

(A) -2
(B) -1
(C) 1
(D) 5

Thanks!!;)

kadence
10-19-2013, 06:57 PM
Solving the following inequality for x
x^2-4x>0
x(x-4)>0
Inserting the roots 0, 4 in the number line below and starting from the right with + since the leading coefficient is positive, we have the following sign diagram.
---(+)--------{0}---------(-)-------------{4}-------(+)---------
So, the inequality holds for x<0 and x>4 and the only value from (A)-(D) which is between 0 and 4 is the value of 1.
Therefore the correct answer is (C).

elizabeth
10-19-2013, 06:58 PM
Thanks Kadence!!