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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
67% (01:33) correct
33%
(01:36)
wrong
based on 58
sessions
History
Date
Time
Result
Not Attempted Yet
If x^2 - 9 = 0 and x < 0, which of the following must be equal to 0 ?
(A) x^2 - 9x
(B) x^2 - 9x + 20
(C) x^2 - 2x + 3
(D) x^2 + 2x - 3
(E) x^2 + 5x + 6
That all being said can't the answer be E as well? And isn't his factoring of E wrong? Thanks
Run
(A) x^2 - 9x
(B) x^2 - 9x + 20
(C) x^2 - 2x + 3
(D) x^2 + 2x - 3
(E) x^2 + 5x + 6
Answer: D
First, find the possible values of x in the given equation. x^2 - 9 = (x + 3)(x - 3), so since that expression is set equal to zero, x could be 3 or -3. Since we're told that x < 0, x must be -3.
There are two ways to identify the correct choice. You can plug -3 into each of the five choices, or you can factor each of the five choices, looking for one that includes the term (x + 3). Try the latter:
(A) = x(x - 9)
(B) = (x - 5)(x - 4)
(C) = (x - 3)(x + 1)
(D) = (x + 3)(x - 1)
(E) = (x + 5)(x + 1)
(D) is correct.
First, find the possible values of x in the given equation. x^2 - 9 = (x + 3)(x - 3), so since that expression is set equal to zero, x could be 3 or -3. Since we're told that x < 0, x must be -3.
There are two ways to identify the correct choice. You can plug -3 into each of the five choices, or you can factor each of the five choices, looking for one that includes the term (x + 3). Try the latter:
(A) = x(x - 9)
(B) = (x - 5)(x - 4)
(C) = (x - 3)(x + 1)
(D) = (x + 3)(x - 1)
(E) = (x + 5)(x + 1)
(D) is correct.
That all being said can't the answer be E as well? And isn't his factoring of E wrong? Thanks
Run
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10 May 2010, 11:55
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run4run
Yes, I have caught errors myself in his questions. I usually just end up sending him an email and he responds that a. he has corrected it or b. there is an oversight. In this case, I think it's the former rather than the latter.
10 May 2010, 12:00
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I agree to.. Ans E also satisfies the condition
x^2-9 = 0
x= +3 or x = -3
if we substitute x= -3 in the equation x^2 +5x+6 = 9-15+6 = 0
E is also the answer
x^2-9 = 0
x= +3 or x = -3
if we substitute x= -3 in the equation x^2 +5x+6 = 9-15+6 = 0
E is also the answer
