What is 2017 doing here?

Algebra Level 3

44 log 11 121 + 6561 log 49 7 = 6605 log X 2017 \large { 44 }^{ \log _{ 11 }{ 121 } } + { 6561 }^{ \log _{ 49 }{ 7 } }=\ \large { 6605 }^{ \log _{ X }{ 2017 } } \

How many values can X X take?

2017 None of the others 3 2 0

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2 solutions

Chew-Seong Cheong
Feb 10, 2017

4 4 log 11 121 + 656 1 log 49 7 = 660 5 log X 2017 4 4 log 11 1 1 2 + 656 1 log 49 49 = 660 5 log X 2017 4 4 2 + 6561 = 660 5 log X 2017 1936 + 81 = 660 5 log X 2017 2017 = 660 5 log X 2017 Note that m log b n = n log b m 2017 = 201 7 log X 6605 log X 6605 = 1 X = 6605 \begin{aligned} 44^{\log_{11}121} + 6561^{\log_{49}7} & = 6605^{\log_X 2017} \\ 44^{\log_{11}11^2} + 6561^{\log_{49}\sqrt{49}} & = 6605^{\log_X 2017} \\ 44^2 + \sqrt{6561} & = 6605^{\log_X 2017} \\ 1936 + 81 & = 6605^{\log_X 2017} \\ 2017 & = \color{#3D99F6} 6605 ^{\log_X 2017} & \small \color{#3D99F6} \text{Note that } m^{\log_b n} = n^{\log_b m} \\ 2017 & = \color{#3D99F6} 2017^{\log_X 6605} \\ \implies \log_X 6605 & = 1 \\ X & = \boxed{6605} \end{aligned}

Therefore, the answer is None of the others \boxed{\text{None of the others}} .

Tom Engelsman
Feb 10, 2017

44 log 11 121 + 6561 log 49 7 = 44 log 11 1 1 2 + 6561 log 49 4 9 0.5 = 4 4 2 + 6561 = 2017. \large { 44 }^{ \log _{ 11 }{ 121 } } + { 6561 }^{ \log _{ 49 }{ 7 } } = \large { 44 }^{ \log _{ 11 }{ 11^{2} } } + { 6561 }^{ \log _{ 49 }{ 49^{0.5} } } = 44^{2} + \sqrt{6561} = 2017. If we now have 2017 = 6605 log X 2017 \large 2017 = { 6605 }^{ \log _{ X }{ 2017 } } , then only X = 6605 X = 6605 solves this equation.

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