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Algebra Level 4

Solve for real x , y , z : x,y,z : { log 2 x + log 4 y + log 4 z = 2 log 3 y + log 9 z + log 9 x = 2 log 4 z + log 16 x + log 16 y = 2 \left\{ \begin{array}{l} \log_2 x+\log_4 y+\log_4 z=2 \\ \log_3 y+\log_9 z+\log_9 x=2 \\ \log_4 z+\log_{16} x+\log_{16} y=2 \\ \end{array} \right. Note: If x = a b , y = c d , z = e f x=\frac{a}{b} , y=\frac{c}{d} , z=\frac{e}{f} , and (a,b) ; (c,d) ; (e;f) are coprime pairs of positive integers, then give a+b+c+d+e+f as the answer.


The answer is 75.

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1 solution

Vilakshan Gupta
Jun 11, 2017

Using log a 2 A = 1 2 log a A \log_{a^{2}}A = \frac{1}{2} \log_{a}A , Three equations can be written as log 2 x y z = 2 log 2 x 2 y z = 4 log 3 y z x = 2 log 3 y 2 z x = 4 log 4 z x y = 2 log 4 z 2 x y = 4 x 2 y z = 2 4 , y 2 z x = 3 4 , z = 2 x y = 4 4 \\ \log_{2}x\sqrt{yz} =2 \\ \implies \log_{2}x^{2}yz = 4 \\ \log_{3}y\sqrt{zx} =2 \\ \implies \log_{3}y^{2}zx = 4 \\ \log_{4}z\sqrt{xy} =2 \\ \implies \log_{4}{z}^{2}xy = 4 \\ \implies x^{2}yz = 2^{4} , y^{2}zx = 3^{4} , z=^{2}xy = 4^{4} \\ Multiplying all these equations,we get ( x y z ) 4 = ( 2 × 3 × 4 ) 4 x y z = 24 T h u s , ( 2 3 4 ) x = 4 2 x = 2 3 , \\ (xyz)^{4}=(2\times 3\times4)^{4} \\ \implies xyz=24 \\ Thus, (2\cdot 3\cdot 4)x = 4^2\Longleftrightarrow x = \frac {2}{3}, \\ Analogously , from other equations , we obtain the answer x = 2 3 , y = 27 8 , z = 32 3 {x = \frac {2}{3},\ y = \frac {27}{8},\ z = \frac {32}{3}} \\ which gives answer as 2 + 3 + 27 + 8 + 32 + 3 = 75 2+3+27+8+32+3 = \boxed {75}

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