Calculator-killer-2

Algebra Level 2

2 16 1 6 2 = 2 2 x \large \dfrac{2^{16}}{16^2} = 2^{2^x}

Find the real number x x .

1 2 4 0 3

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3 solutions

John Frank
Dec 17, 2015

On the left hand side of the equation, we rewrite the denominator as a power of 2. The denominator is 1 6 2 = ( 2 4 ) 2 = 2 8 \displaystyle 16^{2} = (2^{4})^{2} = 2^{8} , so the fraction 2 16 ( 16 ) 2 \frac{2^{16}}{(16)^{2}} cancels out to 2 8 2^{8} .

We take the logarithm with base 2 on both sides of the equation 2 8 = 2 2 x \displaystyle 2^{8} = 2^{2^{x}} , giving 2 x = 8 2^{x} = 8 .

Taking the logarithm with base 2 again, we end up with x = 3 \boxed {x=3} .

Note: exponent towers are evaluated from the top, down. Please see this page: https://brilliant.org/wiki/what-is-a-to-the-b-to-the-c/

I didn't see that "x" was in fact exponent of 2. I took it as (2^2)^x. hence my answer came 4.

Vaibhav Yawalkar - 5 years, 5 months ago

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Yeah I read it as 2^2x ... Looking at it again it is 2^2^x

Josiah McDonald - 5 years, 5 months ago

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This happened with me too. Next time i'll read questions more carefully

Pritish Gulati - 5 years, 5 months ago

the same thing happened to me...

Raymond Cooper - 5 years, 5 months ago

Same can mistake

Shreya Mishra - 5 years, 5 months ago

Sry common

Shreya Mishra - 5 years, 5 months ago
Akshat Sharda
Dec 17, 2015

2 16 1 6 2 = 2 1 6 2 8 = 2 8 2 8 = 2 2 x x = 3 \frac{2^{16}}{16^2}=\frac{2^16}{2^8}=2^8 \\ 2^8=2^{2^x}\Rightarrow x=3

David Molano
Dec 20, 2015

As easy as calculating powers of 2. 2 16 = 65536 = 1000 0 16 2^{16}=65536=10000_{16} and 1 6 2 = 10 0 16 16^2=100_{16} so the quotient becomes 10 0 16 = 2 8 100_{16}=2^8 so x = 3 x=3

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