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Algebra Level 2

Let x x y y and z z all exceed 1, and let w w be a positive number such that log x w = 24 \log_x w = 24 , log y w = 40 \log_y w = 40 and log x y z w = 12 \log_{xyz} w = 12 .

Find log z w \log_{z} w .

Notes : Please don't use a calculator and provide a solution.

61 59 60 58

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1 solution

Chew-Seong Cheong
Nov 18, 2017

It is given that x , y , z > 1 x, y, z > 1 and

{ log x w = 24 log y w = 40 log x y z w = 12 w = { x 24 y 40 ( x y z ) 12 \begin{cases} \log_x w = 24 \\ \log_y w = 40 \\ \log_{xyz} w = 12 \end{cases} \implies w = \begin{cases} x^{24} \\ y^{40} \\ (xyz)^{12} \end{cases}

x 12 y 12 z 12 = x 24 = w y 12 z 12 = x 12 = w 1 2 = y 20 z 12 = y 8 = w 1 5 z 60 = w log z w = 60 \begin{aligned} \implies x^{12}y^{12}z^{12} & = x^{24} = w \\ y^{12}z^{12} & = x^{12} = w^\frac 12 = y^{20} \\ z^{12} & = y^{8} = w^\frac 15 \\ z^{60} & = w \\ \implies \log_z w & = \boxed{60} \end{aligned}

That is what I did! Upvote +1

Michael Wang - 3 years, 3 months ago

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