Find the truth set of the equation x 2 = 3(2x + 9)
MATHEMATICS
WAEC 2014
Find the truth set of the equation x2 = 3(2x + 9)
- A. {x : x = 3, x = 9}
- B. {x : x = -3, x = -9}
- C. {x : x = 3, x = -9}
- D. {x : x = -3, x = 9}
Correct Answer: D. {x : x = -3, x = 9}
Explanation
x2 = 3(2x + 9)
x2 = 6x + 27
x2 - 6x - 27 = 0
x2 - 9x + 3x - 27 = 0
x(x - 9) + 3(x - 9) = (x + 3)(x - 9) = 0
x + 3 = 0 or x - 9 = 0
x = -3 or x = 9
x = -3, x = 9
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