Rod728
Great question! I have a big doubt. For absolute values questions, in which cases do I have to check the solutions? I substituted the value of the 4 solutions in the equation (x=0, x=-4, x=1, and x=-5) and spend some time on it. I know that for this Q when you got the 0 in the solutions, you could stop there, but I'm asking for other questions.
Thanks!
Bunuel
What is the product of all possible solutions of the equation \(|x + 2|^2 - 5|x + 2| = -6\)?
A. -20
B. -5
C. -4
D. 0
E. 20
This is a broad question and depends on several factors, such as the type of question and the approach you're using. Generally, you need to check the solutions when squaring is involved, as it can introduce extraneous solutions. You should also check the solutions when you open the modulus with different signs and you don't consider the ranges beforehand.
For example, if we square |x + 9| = 2x to get rid of the modulus and solve the resulting quadratic equation, x^2 - 6x - 27 = 0, we get x = -3 and x = 9. However, x = -3 does not satisfy |x + 9| = 2x, so only x = 9 is valid. Thus, squaring introduced the extraneous solution x = -3.
Similarly, if we open |x + 9| as x + 9 and -(x + 9) to solve two equations: x + 9 = 2x and -(x + 9) = 2x, we again get two solutions: x = 9 and x = -3. Once more, x = -3 is not valid. In this case, you'd need to plug back the solutions to verify their validity.
The proper approach would be to consider two ranges:
1. When x < -9, x + 9 < 0, so |x + 9| = -(x + 9). Solving -(x + 9) = 2x gives x = -3. However, x = -3 is not in the range x < -9, so it's invalid.
2. When x ≥ -9, x + 9 ≥ 0, so |x + 9| = x + 9. Solving x + 9 = 2x gives x = 9, which is valid for the range x ≥ -9.
With this approach, you compare the solutions with the ranges considered, so you don't need to plug the solutions back into the equation—they are already verified against the ranges.
Hope this clarifies things!
10. Absolute Value
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