JAMB - Mathematics (1990 - No. 19)
Find the solution of the equation x - 8\(\sqrt{x}\) + 15 = 0
3, 5
-3, -5
9, 25
-9, 25
Explanation
x - 8\(\sqrt{x}\) + 15 = 0
x + 15 = 8\(\sqrt{x}\)
square both sides = (x + 15)2 = (8 \(\sqrt{x}\)2
x2 + 225 + 30x = 64x
x2 + 225 + 30x - 64x = 0
x2 - 34x + 225 = 0
(x - 9)(x - 25) = 0
x = 9 or 25
x + 15 = 8\(\sqrt{x}\)
square both sides = (x + 15)2 = (8 \(\sqrt{x}\)2
x2 + 225 + 30x = 64x
x2 + 225 + 30x - 64x = 0
x2 - 34x + 225 = 0
(x - 9)(x - 25) = 0
x = 9 or 25
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