Mathematics
JAMB 2014
A binary operation * is defined by x * y = x
y. If x * 2 = 12 - x, find the possible values of x
-
A.
3,4
-
B.
3,-4
-
C.
-3,4
-
D.
-3,-4
Correct Answer: Option B
Explanation
x * y = x
y
x * 2 = 12 - x
Thus by comparison,
x = x, y = 2
But x * y = x * 2
x
y = 12 - x
x
2 = 12 - x
x
2 + x - 12 = 0
x
2 + 4x - 3x - 12 = 0
x(x + 4) - 3(x + 4) = 0
(x - 3)(x + 4) = 0
x - 3 = 0 or x + 4 = 0
So x = 3 or x = -4
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