GMAT Practice Question: If y=\frac{|3 x-5|}{-x^{2}-3}, for what value of x will the value of y be greatest?
Question
If y=\frac{|3 x-5|}{-x^{2}-3}, for what value of x will the value of y be greatest?
- -5
- -\frac{3}{5}
- 0
- \frac{3}{5}
- \frac{5}{3}
Topics: functions, absolute values, max/min of function
Solution
Step 1
We factor out the negative sign from the denominator to simplify the expression.
y = \frac{\lvert 3x - 5\rvert}{-x^2 - 3} = -\frac{\lvert 3x - 5\rvert}{x^2 + 3}
Step 2
We note that the denominator is always positive, so including the negative sign makes it negative.
x^2 + 3 > 0 -(x^2 + 3) < 0
Step 3
We see that y cannot be positive, so its highest value is zero, which happens when the numerator equals zero.
\lvert 3x - 5\rvert = 0 3x - 5 = 0 3x = 5 x = \frac{5}{3}
Answer
\frac{5}{3}
