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02 Oct 2020, 07:05
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73% (01:12) correct
27%
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02 Oct 2020, 07:15
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BrentGMATPrepNow
What is the value of 2x³ + 6x² - 1?
(1) x(x + 3) = 0
(2) x = 0
(1) x(x + 3) = 0
(2) x = 0
The question stem can be written as 2x³ + 6x² - 1 = 2x² * (x+3)-1 = 2x *x(x+3) - 1
St1- x(x + 3) = 0
Putting the above given condition in expression 2x *x(x+3) - 1, we get answer as -1
St2-x = 0
Putting the above given value in 2x³ + 6x² - 1, we get answer as -1
Hence, both statements are sufficient. Answer D.. IMO
03 Oct 2020, 07:49
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BrentGMATPrepNow
What is the value of 2x³ + 6x² - 1?
(1) x(x + 3) = 0
(2) x = 0
(1) x(x + 3) = 0
(2) x = 0
Target question: What is the value of 2x³ + 6x² - 1?
Statement 1: x(x + 3) = 0
This tells us that EITHER x = 0 OR x = -3
Important: Some students will conclude that, since there are two possible values for x, we can't answer the target question with certainty. However, the target question does not ask us to find the value of x; it asks us to find the value of 2x³ + 6x² - 1.
So, let's evaluate this algebraic expression for both possible x-values
Case a: If x = 0, then 2x³ + 6x² - 1 = 2(0³) + 6(0²) - 1 = -1. In this case, the answer to the target question is 2x³ + 6x² - 1 = -1
Case b: If x = -3, then 2x³ + 6x² - 1 = 2(-3)³ + 6(-3)² - 1 = -54 + 54 - 1 = -1. In this case, the answer to the target question is 2x³ + 6x² - 1 = -1
This means it must be the case that 2x³ + 6x² - 1 = -1
Since we can answer the target question with certainty, statement 1 is SUFFICIENT
Statement 2: x = 0
If x = 0, then 2x³ + 6x² - 1 = 2(0³) + 6(0²) - 1 = -1. In this case, the answer to the target question is 2x³ + 6x² - 1 = -1
Since we can answer the target question with certainty, statement 2 is SUFFICIENT
Answer: D
Cheers,
Brent
