I'm bigger than the Log of Planck constant!

Algebra Level 5

1 0 9 R e ( tan ( 2 + 9 i ) ) \left \lfloor10^9 \ \mathbb{R}e(\tan(2+9i))\right \rfloor

Evaluate the expression above.

Details and Assumptions :

  • i = 1 \displaystyle i=\sqrt{-1}

  • Always use radian values unless stated otherwise.

  • You may use a calculator solve this problem.


The answer is -24.

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1 solution

Ok so we have to find the real part of tan ( 2 + 9 i ) \tan (2+9i)

tan ( 2 + 9 i ) = sin ( 2 + 9 i ) cos ( 2 + 9 i ) = 2 sin ( 2 + 9 i ) cos ( 2 9 i ) 2 cos ( 2 + 9 i ) cos ( 2 9 i ) = sin 4 + sin ( 18 i ) cos 4 + cos ( 18 i ) = sin 4 + i sinh ( 18 ) cos 4 + cosh ( 18 ) \displaystyle \tan (2+9i) \\= \displaystyle \dfrac{\sin (2+9i)}{\cos (2+9i)} \\= \dfrac{2 \sin (2+9i)\cos(2-9i)}{2 \cos (2+9i)\cos(2-9i)} \\= \dfrac{\sin 4+\sin(18i)}{\cos 4+\cos(18i)} \\= \dfrac{\sin 4+i \sinh(18)}{\cos 4+\cosh(18)}

The rest is obvious I guess !

Okay , I'll remember that such an easy question like this touched the 300 point mark ! (305 actually)

EDIT : 310

EDIT 2 : 335

EDIT 3 : 380 !

A Former Brilliant Member - 6 years, 2 months ago

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The reason is 2% rule. Approximation on B'ant is valid for ±2% of answer. Many people answered 0 which is incorrect as answer itself is too small

Pranjal Jain - 6 years, 2 months ago

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Oh , thanks ! I didn't know of this fact :)

A Former Brilliant Member - 6 years, 2 months ago

Actually , the digital sum of my JEE roll number is 29 , so that's the inspiration for this question !

A Former Brilliant Member - 6 years, 3 months ago

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Feeling pressure for JEE? Last question? Really? That's sad! But joy and happiness are coming shortly in your life! I hope for the best!

Kartik Sharma - 6 years, 3 months ago

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Thanks a lot !

A Former Brilliant Member - 6 years, 3 months ago

What identity is that in the third to last line?

Trevor Arashiro - 6 years, 2 months ago

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First of all I had multiplied and divided the term cos ( 2 9 i ) \cos (2-9i) .

Now I have used the following identities :

  • sin ( A + B ) + sin ( A B ) = 2 sin A cos B \sin (A+B) + \sin (A-B) = 2\sin A \cos B

  • cos ( A + B ) + cos ( A B ) = 2 cos A cos B \cos (A+B) + \cos (A-B) = 2\cos A \cos B

A Former Brilliant Member - 6 years, 2 months ago

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