Adding 42 to a given positive number gives the same result as squaring the number.
MATHEMATICS
WAEC 2015
Adding 42 to a given positive number gives the same result as squaring the number. Find the number
- A. 14
- B. 13
- C. 7
- D. 6
Correct Answer: C. 7
Explanation
Let the given positive number be x
Then 4 + x = x2
0 = x2 - x - 42
or x2 - x - 42 = 0
x2 - 7x + 6x - 42 = 0
x(x - 7) + 6(x - 7) = 0
= (x + 6)(x - 7) = 0
x = -6 or x = 7
Hence, x = 7
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