Practice test 2 question 1

[domivantman]

Quantity A: |x3 + 2|
Quantity B: |x|

Quantity A means x3+2>0 or x3+2<0
x>cubic root of 2 so x >1.2599 and
x< cubit root of -2 so x< -1.2599

The explanation uses –1 which is not on the range so I don't understand why the use that number to prove D.

Can someone please help me understand this question, because my answer was A and not D, since -1 is not on the range of quantity A.

[tommywallach]

Hey Domivant,

Sounds like you're a little confused on the rules of Quantitative Comparison, also on the difference between an equation and an expression.

x^3 +2

THIS IS NOT AN EQUATION. It's an expression. It's only an equation if it has an EQUAL sign (or an INEQUALITY sign).

You took an expression and pretended it was an equation. Basically, you decided to set it greater than/less than zero. But you see how you just made that up? The question didn't have it. So why are you suddenly defining the range of something, when the question didn't define it?

lx^3 + 2l is not the same as lx^3 +2] < 0

One of them is an expression, one is an equation.

All you can do to compare these two columns is to start picking values for x and see what happens to the expressions.

-t

[domivantman]

Thank you very much!

[tommywallach]

Glad to help! Though I noticed the lowercase L's I tried to use for absolute values symbols DID NOT WORK!

-t