Inspired by Kenny Lau

Geometry Level 4

If the value of tan ( i ) \tan(i) can be expressed as a point ( a , b ) (a,b) on the Argand Plane, find the distance of the point ( a , b ) (a,b) from the origin.

Details and Assumptions

  • a , b R a,b \in \mathbb{R}

  • 1 = i \sqrt{-1} = i

  • Round your answer to 3 decimal places.


Inspiration


The answer is 0.762.

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1 solution

By Euler's Formula,

e i θ = cos ( θ ) + i sin ( θ ) e^{i\theta} = \cos(\theta) + i\sin(\theta)

e i θ = cos ( θ ) i sin ( θ ) \Rightarrow e^{-i\theta} = \cos(\theta) - i\sin(\theta)

Hence,

e i θ + e i θ = 2 cos ( θ ) e^{i\theta} + e^{-i\theta} = 2\cos(\theta)

And similarly,

e i θ e i θ = 2 i sin ( θ ) e^{i\theta} - e^{-i\theta} = 2i\sin(\theta)

Dividing these two equations,

e i θ e i θ e i θ + e i θ = i tan ( θ ) \dfrac{e^{i\theta} - e^{-i\theta}}{e^{i\theta} + e^{-i\theta}} = i\tan(\theta)

tan ( i ) = i e 1 e e + 1 e 0.762 i \tan(i) = i\dfrac{e - \frac{1}{e}}{e + \frac{1}{e}} \approx 0.762i

On the Argand Plane, this is nothing but ( 0 , 0.762 ) (0,0.762) .

Hence the distance is: 0.762 \boxed{0.762} .

Thank you for your dedication!

Kenny Lau - 5 years, 10 months ago

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You are welcome. Cheers.

Vishwak Srinivasan - 5 years, 10 months ago

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