Bromance <3

Geometry Level 3

Cody Song wants to buy Zi Song chocolates for Valentine's Day. Cody Song has tan 8 π 24 + tan 8 5 π 24 + tan 8 7 π 24 + tan 8 11 π 24 \tan^8\frac\pi{24}+\tan^8\frac{5\pi}{24}+\tan^8\frac{7\pi}{24}+\tan^8\frac{11\pi}{24} in dollars. But, chocolates cost $ 19204 \$19204 each (they're gourmet). How many chocolates can Cody buy Zi Song?


The answer is 577.

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1 solution

Saurabh Mallik
Mar 27, 2014

To find the number of chocolates we need to do this:

= Total money/Cost of each chocolate

= t a n 8 × p i 24 + t a n 8 × 5 × p i 24 + t a n 8 × 7 × p i 24 + t a n 8 × 11 × p i 24 19204 = 11080708 19204 = \frac {tan^{8} \times \frac{pi}{24}+tan^{8} \times \frac{5 \times pi}{24}+tan^{8} \times \frac{7 \times pi}{24}+tan^{8} \times \frac{11 \times pi}{24}}{19204} = \frac{11080708}{19204} = 577 = 577

So, the number of chocolates he can buy is 577 \boxed{577} .

This problem can be solved without the use of a calculator.

Pi Han Goh - 7 years, 2 months ago

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Notice that cot ( π 2 x ) = tan x \cot\left(\frac\pi2-x\right)=\tan x . Hence,

tan 8 π 24 + tan 8 5 π 24 + tan 8 7 π 24 + tan 8 11 π 24 = tan 8 π 24 + tan 8 5 π 24 + cot 8 7 π 24 + cot 8 11 π 24 \tan^8\frac{\pi}{24}+\tan^8\frac{5\pi}{24}+\tan^8\frac{7\pi}{24}+\tan^8\frac{11\pi}{24}=\tan^8\frac{\pi}{24}+\tan^8\frac{5\pi}{24}+\cot^8\frac{7\pi}{24}+\cot^8\frac{11\pi}{24}

Letting x = tan π 24 x=\tan\frac\pi{24} and y = tan 5 π 24 y=\tan\frac{5\pi}{24} , we get x 8 + 1 x 8 + y 8 + 1 y 8 x^8+\frac1{x^8}+y^8+\frac1{y^8} . But

x 8 + 1 x 8 = ( x 4 + 1 x 4 ) 2 2 = ( ( x 2 + 1 x 2 ) 2 2 ) 2 2 = ( ( ( x + 1 x ) 2 2 ) 2 2 ) 2 2 x^8+\frac1{x^8}=\left(x^4+\frac1{x^4}\right)^2-2=\left(\left(x^2+\frac1{x^2}\right)^2-2\right)^2-2=\left(\left(\left(x+\frac1x\right)^2-2\right)^2-2\right)^2-2

Similarly,

y 8 + 1 y 8 = ( ( ( y + 1 y ) 2 2 ) 2 2 ) 2 2 y^8+\frac1{y^8}=\left(\left(\left(y+\frac1y\right)^2-2\right)^2-2\right)^2-2

Hence, it suffices to find x + 1 x x+\frac1x and y + 1 y y+\frac1y . So tan π 24 + 1 tan π 24 = 1 sin π 24 cos π 24 = 2 sin π 12 \tan\frac\pi{24}+\frac1{\tan\frac\pi{24}}=\frac1{\sin\frac{\pi}{24}\cos\frac\pi{24}}=\frac{2}{\sin\frac{\pi}{12}} . Similarly, tan 5 π 24 + 1 tan 5 π 24 = 2 sin 5 π 12 \tan\frac{5\pi}{24}+\frac1{\tan\frac{5\pi}{24}}=\frac{2}{\sin\frac{5\pi}{12}} . But sin π 12 = 6 2 4 \sin\frac{\pi}{12}=\frac{\sqrt6-\sqrt2}4 and sin 5 π 12 = 6 + 2 4 \sin\frac{5\pi}{12}=\frac{\sqrt6+\sqrt2}4 so x + 1 x = 2 ( 6 + 2 ) x+\frac1x=2\left(\sqrt6+\sqrt2\right) and y + 1 y = 2 ( 6 2 ) y+\frac1y=2\left(\sqrt6-\sqrt2\right) . Using the formulas above, we can easily compute that x 8 + 1 x 8 + y 8 + 1 y 8 = 11080708 x^8+\frac1x^8+y^8+\frac1y^8=11080708 .

Cody Johnson - 7 years, 2 months ago

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I know what is bromance means but your problem sounds *** \text{***} to me. :D

Tunk-Fey Ariawan - 7 years, 2 months ago

If he would have known this method, then definitely he would have posted a better solution than mine. But thanks! Cody Johnson. :D

Saurabh Mallik - 7 years, 2 months ago

Does tan 8 π 24 + tan 8 5 π 24 + tan 8 7 π 24 + tan 8 11 π 24 = tan 8 π 24 + tan 8 5 π 24 + cot 8 5 π 24 + cot 8 π 24 \tan^8 \dfrac{\pi}{24}+\tan^8 \dfrac{5\pi}{24}+\tan^8 \dfrac{7\pi}{24}+\tan^8 \dfrac{11\pi}{24}=\tan^8 \dfrac{\pi}{24} + \tan^8 \dfrac{5\pi}{24} +\cot^8 \dfrac{5\pi}{24} + \cot^8 \dfrac{\pi}{24} help?

Hahn Lheem - 7 years, 2 months ago

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yes, u r right....

Vighnesh Raut - 7 years, 2 months ago

Would you also like to post a solution?

Saurabh Mallik - 7 years, 2 months ago

Can somebody help me find solutions to this question?

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Saurabh Mallik - 7 years, 2 months ago

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Why are you posting this everywhere?

Sreejato Bhattacharya - 7 years, 2 months ago

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I'm not able to solve these anagrams. That's why I posted it everywhere. Can anybody please help me regarding this?

Saurabh Mallik - 7 years, 2 months ago

Maybe this help: Anagram Solver . Just input your anagrams there and see the appropriate output.

Tunk-Fey Ariawan - 7 years, 2 months ago

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