\(\mathrm{g(x) = (x - 2)(x + 1)(x - 5)}\)The function g is given. Which table of values represents \(\mathrm{y =...
GMAT Advanced Math : (Adv_Math) Questions
The function g is given. Which table of values represents \(\mathrm{y = g(x) + 4}\)?
| x | y |
|---|---|
| 2 | 4 |
| 0 | 14 |
| -1 | 4 |
| x | y |
|---|---|
| 2 | 0 |
| 0 | 10 |
| -1 | 0 |
| x | y |
|---|---|
| 2 | -4 |
| 0 | 6 |
| -1 | -4 |
| x | y |
|---|---|
| 2 | 8 |
| 0 | 20 |
| -1 | 8 |
1. INFER the key insight about polynomial roots
- Given: \(\mathrm{g(x) = (x - 2)(x + 1)(x - 5)}\) in factored form
- Key insight: When a polynomial is factored, the roots (where \(\mathrm{g(x) = 0}\)) occur when each factor equals zero:
- \(\mathrm{x - 2 = 0}\) → \(\mathrm{x = 2}\), so \(\mathrm{g(2) = 0}\)
- \(\mathrm{x + 1 = 0}\) → \(\mathrm{x = -1}\), so \(\mathrm{g(-1) = 0}\)
- \(\mathrm{x - 5 = 0}\) → \(\mathrm{x = 5}\), so \(\mathrm{g(5) = 0}\)
2. TRANSLATE the transformation requirement
- We need \(\mathrm{y = g(x) + 4}\), not just \(\mathrm{g(x)}\)
- This means: take each \(\mathrm{g(x)}\) value and add 4 to get the corresponding y-value
3. SIMPLIFY the evaluation at each x-value
- At \(\mathrm{x = 2}\): \(\mathrm{g(2) = 0}\), so \(\mathrm{y = 0 + 4 = 4}\)
- At \(\mathrm{x = -1}\): \(\mathrm{g(-1) = 0}\), so \(\mathrm{y = 0 + 4 = 4}\)
- At \(\mathrm{x = 0}\):
\(\mathrm{g(0) = (0-2)(0+1)(0-5)}\)
\(\mathrm{= (-2)(1)(-5)}\)
\(\mathrm{= 10}\)
so \(\mathrm{y = 10 + 4 = 14}\)
4. INFER which table matches our calculated values
- We need the table showing: \(\mathrm{(2,4), (0,14), (-1,4)}\)
- This matches Choice A exactly
Answer: A
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak TRANSLATE skill: Students misread or misunderstand what \(\mathrm{y = g(x) + 4}\) means and think they need to find values for \(\mathrm{g(x)}\) instead of \(\mathrm{g(x) + 4}\).
They correctly identify that \(\mathrm{g(2) = 0}\), \(\mathrm{g(-1) = 0}\), and \(\mathrm{g(0) = 10}\), but forget to add 4 to each value. This leads them to look for a table with values \(\mathrm{(2,0), (0,10), (-1,0)}\).
This may lead them to select Choice B.
Second Most Common Error:
Poor SIMPLIFY execution: Students make arithmetic errors when calculating \(\mathrm{g(0) = (0-2)(0+1)(0-5)}\), possibly getting the wrong sign or missing a step in the multiplication.
If they calculate \(\mathrm{g(0)}\) incorrectly as -10 instead of 10, then \(\mathrm{y = -10 + 4 = -6}\), leading them toward an incorrect table choice. This causes confusion and potentially random guessing among the remaining choices.
The Bottom Line:
This problem tests whether students can correctly apply function transformations while managing the details of polynomial evaluation. Success requires both understanding what the transformation means AND executing the arithmetic correctly.
| x | y |
|---|---|
| 2 | 4 |
| 0 | 14 |
| -1 | 4 |
| x | y |
|---|---|
| 2 | 0 |
| 0 | 10 |
| -1 | 0 |
| x | y |
|---|---|
| 2 | -4 |
| 0 | 6 |
| -1 | -4 |
| x | y |
|---|---|
| 2 | 8 |
| 0 | 20 |
| -1 | 8 |