For the linear function g, the graph of \(\mathrm{y = g(x)}\) in the xy-plane has a slope of 2 and...
GMAT Algebra : (Alg) Questions
For the linear function g, the graph of \(\mathrm{y = g(x)}\) in the xy-plane has a slope of 2 and passes through the point \(\mathrm{(1, 14)}\). Which equation defines g?
\(\mathrm{g(x) = 2x}\)
\(\mathrm{g(x) = 2x + 2}\)
\(\mathrm{g(x) = 2x + 12}\)
\(\mathrm{g(x) = 2x + 14}\)
1. TRANSLATE the problem information
- Given information:
- Slope = 2
- Graph passes through point (1, 14)
- Need to find equation g(x)
2. INFER the approach
- Since this is a linear function with known slope, use slope-intercept form
- Set up: \(\mathrm{g(x) = mx + b}\) where \(\mathrm{m = 2}\)
- This gives us: \(\mathrm{g(x) = 2x + b}\)
- Now need to find the y-intercept b using the given point
3. TRANSLATE the point condition into an equation
- "Passes through (1, 14)" means when \(\mathrm{x = 1, g(x) = 14}\)
- Substitute into our equation: \(\mathrm{14 = 2(1) + b}\)
4. SIMPLIFY to find b
- \(\mathrm{14 = 2(1) + b}\)
- \(\mathrm{14 = 2 + b}\)
- \(\mathrm{b = 14 - 2 = 12}\)
5. Write the final equation
- \(\mathrm{g(x) = 2x + 12}\)
Answer: C. g(x) = 2x + 12
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak INFER skills: Students see the point (1, 14) and think the y-intercept b must equal 14, without recognizing they need to substitute the point into the equation to solve for b.
They incorrectly reason: "The function passes through (1, 14), so the equation must have 14 in it somewhere." This leads them to select Choice D (g(x) = 2x + 14).
Second Most Common Error:
Poor SIMPLIFY execution: Students correctly set up \(\mathrm{14 = 2 + b}\) but make arithmetic errors, such as adding instead of subtracting: \(\mathrm{b = 14 + 2 = 16}\).
Since 16 isn't among the y-intercept values in the choices, this leads to confusion and guessing.
The Bottom Line:
This problem tests whether students understand that "passing through a point" creates a constraint equation that must be solved, rather than directly incorporating the point's coordinates into the final answer.
\(\mathrm{g(x) = 2x}\)
\(\mathrm{g(x) = 2x + 2}\)
\(\mathrm{g(x) = 2x + 12}\)
\(\mathrm{g(x) = 2x + 14}\)