lo g 2 x + lo g 4 y + lo g 4 z lo g 3 y + lo g 9 z + lo g 9 x lo g 4 z + lo g 1 6 x + lo g 1 6 y = = = 2 2 2
Solve the system equations where x , y and z are positive real numbers.
If the value x , y , z can be written in the form b x a x , b y a y , b z a z for co-prime a i , a j , find the value of a x + b x + a y + b y + a z + b z .
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The given equations are
The first equation can be written as
lo g 2 x + lo g 4 y + lo g 4 z = lo g 4 x 2 y x = 2 ⇒ x 2 y z = 2 4 . . . . . . . . . . . . 1
Similarly,
lo g 3 y + lo g 9 z + lo g 9 x = 2 = lo g 9 y 2 x z ⇒ y 2 z x = 3 4 . . . . . . . . . . . . 2
Similarly,
lo g 4 z + lo g 1 6 x + lo g 1 6 y = 2 = lo g 1 6 z 2 x y ⇒ z 2 x y = 1 6 2 = 4 4 . . . 3
Multiplying 1 , 2 , 3 ,we get,
( x y z ) 4 = 2 4 × 3 4 × 4 4 = ( 2 4 ) 4 ⇒ x y z = 2 4
Then 1 becomes x 2 y z = 1 6 ⇒ x ( x y z ) = 1 6 ⇒ x = 2 4 1 6 ⇒ x = 3 2
Similarly 2 becomes y 2 x z = 8 1 ⇒ y ( x y z ) = 8 1 ⇒ y = 2 4 8 1 ⇒ y = 8 2 7
Similarly 3 becomes z 2 x y = 2 5 6 ⇒ z ( x y z ) = 2 5 6 ⇒ z = 2 4 2 5 6 ⇒ z = 3 3 2
Therefore the answer is 2 + 3 + 2 7 + 8 + 3 2 + 3 = 7 5 .
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We can rewrite the equations as following
lo g 2 x + lo g 4 y + lo g 4 z = lo g 4 x 2 y z = 2 ⇒ x 2 y z = 2 4
lo g 3 y + lo g 9 z + lo g 9 x = lo g 9 y 2 z x = 2 ⇒ y 2 z x = 3 4
lo g 4 z + lo g 1 6 x + lo g 1 6 y = lo g 1 6 z 2 x y = 2 ⇒ z 2 x y = 4 4
We multiply the solutions together to get that ( x y z ) 4 = 2 4 4 ⇒ x y z = 2 4
From this it's easy to get the values of x , y , z which are equal to 3 2 , 8 2 7 , 3 3 2 respectively.
Therefore the answer is 2 + 3 + 2 7 + 8 + 3 2 + 3 = 7 5 .