1.

What is the value of cot (– 870º)?

Answer»

cot (– 870°) = – cot 870°               ( cot (– θ) = – cot θ) 

= – cot (720° + 150°) = – cot (2 x 360° + 150°)

= – cot 150° = – cot (90° + 60°)          ( cot (n .360° + θ) = cot θ, n ∈ N) 

= – (– tan 60°)                          (cot (90° + θ) = – tan θ) 

= tan 60° = √3 .



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