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secondary 3 | A Maths
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Since log x y and log y x are reciprocals,
Let log x y = u
2u + 2/u = 5
2u2 + 2 = 5u
2u2 - 5u + 2 = 0
(2u - 1) (u - 2) = 0
u = 1/2 or u = 2
This means that
log x y = 1/2 or log x y = 2
Converting to index,
x^1/2 = y or x^2 = y
x = y^2 or x^2 = y
For each case, we solve the equation together with the other equation xy = 8.
For x = y^2,
y^2 * y = 8
y^3 = 8
y = 2
x = 2^2 = 4
For x^2 = y,
x * x^2 = 8
x^3 = 8
x = 2
y = 2^2 = 4
The solutions sets are x = 4, y = 2 or x = 2, y = 4 (which are expected to be symmetrical since the equations are symmetrical)
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