WAEC 2022 Mathematics · Question 32
Solve 6x = 5x - 1
Options
- A.x = 2,3
- B.x = 0,3
- C.x = ,
- D.x = ,
Answer: C. x = ,
Explanation written with AI and checked against the answer key
Analyze the question: We need to find the values of x that satisfy the quadratic equation 6x² = 5x − 1.
Concept: Move every term to one side so the equation equals zero (ax² + bx + c = 0), then factorise.
Solution:
- Rearrange: 6x² − 5x + 1 = 0
- Factorise by finding two numbers that multiply to 6 × 1 = 6 and add to −5. These are −2 and −3.
- Split the middle term: 6x² − 2x − 3x + 1 = 0
- Group: 2x(3x − 1) − 1(3x − 1) = 0
- Factor out the common bracket: (3x − 1)(2x − 1) = 0
- Set each factor to zero: • 3x − 1 = 0 → x = 1/3 • 2x − 1 = 0 → x = 1/2
Check:
- x = 1/2: 6(1/4) = 1.5 and 5(1/2) − 1 = 1.5 ✓
- x = 1/3: 6(1/9) = 2/3 and 5(1/3) − 1 = 2/3 ✓
Answer: C
Tip: After rearranging, you can quickly test the options by substituting them back. Also, if the middle term is negative and the last term is positive (like −5x and +1), both roots will be positive. That immediately rules out option D, which has a negative root. For options A and B, the values 2, 3, and 0 are too large or don't work, so you can eliminate them fast.
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