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29 May 2020, 09:55
Kudos
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A
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% (02:05) correct
33%
(02:15)
wrong
based on 847
sessions
History
Date
Time
Result
Not Attempted Yet
What is the product of the roots of \(x^2 – 7|x| - 30 = 0\)?
A. -100
B. -9
C. 0
D. 9
E. 100
A. -100
B. -9
C. 0
D. 9
E. 100
29 May 2020, 10:01
Kudos
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Bunuel
\(x^2 – 7|x| - 30 = 0\)
i.e. \(lxl^2 – 7|x| - 30 = 0\)
i.e. \(lxl^2 – 10|x| + 3|x| - 30 = 0\)
i.e. \( (lxl – 10)*(|x| + 3) = 0\)
i.e lxl = 10 or -3
But lxl can NOT be negative hence it can NOT be -3
i.e. lxl = 10
i.e. x = +10 or -10
Product of the roots = (+10)*(-10) = -100
ANswer: Option A
General Discussion
29 May 2020, 10:05
Kudos
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\(x^2-7|x|-30\) ----eqn(1). We need to check for two values of |x|.
When x>0, solving eqn(1) we get x=10
When x<0, the value of x will be negation of what we obtained for x>0. Thus, we get x=-10.
Product of roots: -100.
When x>0, solving eqn(1) we get x=10
When x<0, the value of x will be negation of what we obtained for x>0. Thus, we get x=-10.
Product of roots: -100.
