GreenlightTestPrep wrote:
If |3−3x2|≥1, which of the following is NOT a possible value of x?
A) −43
B) −13
C) 43
D) 53
E) 83
STRATEGY: As with all GRE Multiple Choice questions, we should immediately ask ourselves, Can I use the answer choices to my advantage?
In this case, we could test the answer choices, but doing so would involve evaluating fractions within fractions, which would be quite time-consuming.
Now we should give ourselves about 10-20 seconds to identify a faster approach.
In this case, it will likely be faster to use algebra to solve the given inequality for x. So let's do that. Two properties involving absolute value inequalities:
Property #1: If |something| < k, then –k < something < k
Property #2: If |something| > k, then EITHER something > k OR something < -k Note: these rules assume that k is positiveThe given inequality is in the form of
Property #2, which means...
Either
3−3x2≥1 or
3−3x2≤−1.
Let's solve each inequality for
xTake:
3−3x2≥1Subtract
3 from both sides:
−3x2≥−2Multiply both sides by
2 to get:
−3x≥−4Divide both sides by
−3 to get:
x≤43 [ since we divided both sides of the inequality by a negative value, we reversed the direction of the inequality symbol]Take:
3−3x2≤−1Subtract
3 from both sides:
−3x2≤−4Multiply both sides by
2 to get:
−3x≤−8Divide both sides by
−3 to get:
x≥83 If
x≤43 or
x≥83, then
x cannot equal
53Answer: D