Select for a and for b values such that the equation x/a = x - b has more than one...
GMAT Two Part Analysis : (TPA) Questions
Select for a and for b values such that the equation \(\frac{\mathrm{x}}{\mathrm{a}} = \mathrm{x} - \mathrm{b}\) has more than one solution for \(\mathrm{x}\).
Make only two selections, one in each column.
Phase 1: Owning the Dataset
Understanding the Equation
We need to find values of a and b such that the equation \(\mathrm{x/a = x - b}\) has more than one solution for x.
Visual Representation
For this algebraic problem, let's use equation format to track our transformations:
Original: \(\mathrm{x/a = x - b}\)
down arrow
Goal: Find a and b that give MORE THAN ONE solution
Phase 2: Understanding the Question
Key Insight About Solutions
For a linear equation in one variable, we can have:
- No solution (contradiction like \(\mathrm{0 = 5}\))
- Exactly one solution (typical case)
- Infinitely many solutions (identity like \(\mathrm{x = x}\))
"More than one solution" means infinitely many solutions, which happens when our equation becomes an identity.
Working with the Equation
Let's manipulate \(\mathrm{x/a = x - b}\) algebraically.
Multiplying both sides by a (assuming \(\mathrm{a ≠ 0}\)):
\(\mathrm{x = a(x - b)}\)
\(\mathrm{x = ax - ab}\)
\(\mathrm{x - ax = -ab}\)
\(\mathrm{x(1 - a) = -ab}\)
Critical Analysis
If \(\mathrm{a ≠ 1}\), we can divide by \(\mathrm{(1 - a)}\):
\(\mathrm{x = -ab/(1 - a)}\)
This gives exactly ONE solution - not what we want.
If \(\mathrm{a = 1}\), then:
\(\mathrm{x(1 - 1) = -1 × b}\)
\(\mathrm{x × 0 = -b}\)
\(\mathrm{0 = -b}\)
This means b must equal 0.
Phase 3: Finding the Answer
Verification
When \(\mathrm{a = 1}\) and \(\mathrm{b = 0}\):
\(\mathrm{x/1 = x - 0}\)
\(\mathrm{x = x}\)
This is an identity! It's true for ALL values of x, giving us infinitely many solutions.
Checking Our Answer Choices
From [-2, -1, 0, 1, 2]:
- For a: We need 1 tick mark
- For b: We need 0 tick mark
Both values are available in our choices.
Phase 4: Solution
Final Answer:
- Select 1 for a
- Select 0 for b
This makes the equation \(\mathrm{x/1 = x - 0}\), which simplifies to \(\mathrm{x = x}\), an identity true for all x values, giving us infinitely many solutions.