A big what

Geometry Level 3

What is the value of tan ( 7 5 ) + cot ( 7 5 ) \tan(75^\circ)+\cot(75^\circ) ?

1 4 0 -4

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2 solutions

=2+√3+2-√3=4

Moderator note:

Can you solve this problem without knowing neither values of tan ( 7 5 ) , cot ( 7 5 ) \tan(75^\circ), \cot(75^\circ ) ?

In response to the Challenge Master: Generalising,

tan θ + cot θ = sin θ cos θ + cos θ sin θ = sin 2 θ + cos 2 θ sin θ cos θ = 2 csc 2 θ \tan\theta+\cot\theta=\frac{\sin\theta}{\cos\theta}+\frac{\cos\theta}{\sin\theta}=\frac{\sin^{2}\theta+\cos^{2}\theta}{\sin\theta\cos\theta}=2\csc2\theta

Omkar Kulkarni - 6 years ago

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=2/sin30=4 good!

Mohamed Ameén - 6 years ago

Use tan(A+B) formula

Ahmed Nawaz Usmani - 4 years, 6 months ago
Stewart Gordon
May 17, 2015

It's a simple process of elimination. If θ ( 0 , π 2 ) \theta \in (0, \frac\pi2) then tan θ > 0 \tan \theta > 0 , therefore cot θ > 0 \cot \theta > 0 . And it can't be 1, because then it would have to be 0 + 1 0 + 1 or the sum of two numbers in ( 0 , 1 ) (0, 1) , either of which is impossible if one is the reciprocal of the other.

They are not always greater than 0 between 0 n 90

Ahmed Nawaz Usmani - 4 years, 6 months ago

Would you care to give a counterexample Ahmed?

Stewart Gordon - 4 years, 6 months ago

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