Trigonometry Crush 7

Geometry Level 3

A = tan ( 6 ) tan ( 4 2 ) , B = cot ( 6 6 ) cot ( 7 8 ) \large A=\tan(6^\circ) \tan(42^\circ) \qquad, \qquad B=\cot(66^\circ) \cot(78^\circ)

Which of these numbers are larger?

B B A A They are both equal There is insufficient information

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3 solutions

Raj Rajput
Aug 23, 2015

Amazing solution to a good problem.....upvoted

Abhilash Sabapaty - 5 years, 9 months ago

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Thanks :) :)

RAJ RAJPUT - 5 years, 9 months ago

Brilliant solution, Raj.

John King - 5 years, 9 months ago

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Thanks :) :)

RAJ RAJPUT - 5 years, 9 months ago

Good use of a nice identity. Good work @Raj Rajput . upvoted!!

Nelson Mandela - 5 years, 9 months ago

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Thanks @Nelson Mandela

RAJ RAJPUT - 5 years, 9 months ago

But if we use calculator we get a different answer????

Riddhesh Deshmukh - 5 years, 8 months ago

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But why you are approaching this with calculator ? Anyways we get same answer from calculator also :)

RAJ RAJPUT - 5 years, 8 months ago

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will you post it pls

Riddhesh Deshmukh - 5 years, 8 months ago

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@Riddhesh Deshmukh ya use scientific calculator for getting values of tan6 and tan42 then for cot convert it into tan form using 90-(angle) then calculate and then divide you will get it :)

RAJ RAJPUT - 5 years, 8 months ago

Awesome work as always dude.Upvoted!

Athiyaman Nallathambi - 5 years, 9 months ago

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Thanks :) but i didn't get your upvote lol :)

RAJ RAJPUT - 5 years, 9 months ago

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lol sorry about that.Now i can say Upvoted! :)

Athiyaman Nallathambi - 5 years, 9 months ago

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@Athiyaman Nallathambi Thank you :) :)

RAJ RAJPUT - 5 years, 9 months ago
Otto Bretscher
Aug 26, 2015

Let t = π 15 = 1 2 o t=\frac{\pi}{15}=12^o throughout. We need to show that tan ( t ) tan ( 2 t ) tan ( 4 t ) tan ( 7 t ) = 1. \tan(t)\tan(2t)\tan(4t)\tan(7t)=1. We have the product formulas k = 1 7 tan ( k t ) = 15 \prod_{k=1}^7\tan(kt)=\sqrt{15} and k = 1 2 tan ( 3 k t ) = 5 \prod_{k=1}^2\tan(3kt)=\sqrt{5} . If we divide the first equation by the second and also by tan ( π / 3 ) = 3 \tan(\pi/3)=\sqrt3 , the claim follows.

Challenge Master Note: WOW How did you know what angles and products to use?

Pi Han Goh - 5 years, 9 months ago

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As you know, I try to solve all trigonometry problems this way. These product formulas for sin, cos, and tan are basically all the trig identities I know ;)

Otto Bretscher - 5 years, 9 months ago
Hadia Qadir
Aug 30, 2015

Expression A = Expression B

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