OokandGluk
gmatophobia
Bunuel
If \(\frac{\sqrt{x^2}}{\sqrt[3]{x^3}}=-1\) and \(x \neq 0\), what is the value of \(\frac{2|x| + 6}{3 - x}\) ?
A. -2
B. 1
C. 2
D. 3
E. Cannot be determined from the given information
\(\frac{\sqrt{x^2}}{\sqrt[3]{x^3}}\)
= \(\frac{|x|}{x}\)
\(\frac{|x|}{x} = -1\)
Hence, we can infer that that \(x\) is negative.
Let's assume \(x = -1\)
= \(\frac{2|x| + 6}{3 - x}\)
= \(\frac{2|-1| + 6}{3 - (-1)}\)
= \(\frac{8}{4}\)
= \(2\)
Option CI have a doubt. The numerator can be either postive or negative for every case of denominator can only be positive or negative.
In that case, won't the equation be always either 1 or -1. Instead of only -1. This leads to an undefined behaviour right?
Bunuel Can you please help?
\(\sqrt{x^2} = |x|\) and |x| cannot be negative. Generally, the square root sign always indicates non-negative square root.
Mathematically, \(\sqrt{...}\) is the square root sign, a function (called the principal square root function), which cannot give negative result. So, this sign (\(\sqrt{...}\)) always means non-negative square root.
The graph of the function f(x) = √xNotice that it's defined for non-negative numbers and is producing non-negative results.
TO SUMMARIZE:
When the GMAT (and generally in math) provides the square root sign for an even root, such as a square root, fourth root, etc. then the only accepted answer is the non-negative root. That is:
√9 = 3, NOT +3 or -3;
\(\sqrt[4]{16} = 2\), NOT +2 or -2;
Notice that in contrast, the equation x^2 = 9 has TWO solutions, +3 and -3. Because x^2 = 9 means that x =-√9 =-3 or x = √9 = 3.
Hope it helps.