If x > y > 1 and lo g x y 1 + lo g y x 1 = 2 0 2 9 , find the value of lo g x y x 1 − lo g x y y 1 .
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Check the answer please, I think it's − 4 5
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So sorry for that.... It was too late when I typed the solution and felt sleepy so I thought to edit the solution in morning so now I have edited it.
The answer is definitely -45. Note how the first fraction has a larger denominator, and thus is smaller, than the second one. Which is why the answer should be negative.
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So sorry for that.... It was too late when I typed the solution and felt sleepy so I thought to edit the solution in morning so now I have edited it.
Nice question
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First simplify few things...
( 1 ) Recall lo g a b = lo g b a 1
& ( 2 ) Substitute lo g y x = q .
The given equation is:
q + q 1 lo g y x + lo g y x 1 = 2 0 2 9
And required expression is :
lo g x x y − lo g y x y = ( 1 + lo g x y ) − ( 1 + lo g y x )
which is same as lo g x y − lo g y x = q 1 − q . Hence the question translates to:
Given : q + q 1 = 2 0 2 9 , q 1 − q = ?
Now we know:
q 1 − q = − ( q + q 1 ) 2 − 4 = − ( 2 0 2 9 ) − 4 = − 4 5
NOTE:- Since x > y ,
lo g y x > 1 ⟹ ( lo g y x ) 2 > 1 ⟹ q 2 > 1 ⟹ q > q 1 ⟹ q 1 − q < 0