Posted by **dan** on Wednesday, January 23, 2013 at 9:47pm.

cos 17pi/6 + tan 17pi/6

- Trigonometry -
**Reiny**, Wednesday, January 23, 2013 at 10:27pm
Perhaps you might find it easier to think in degrees ?

17π/6 radians = 510°

which is coterminal with 150°

cos 150° = - cos30° = -√3/2 , by CAST rule

tan 150 = - tan30 = -1/√3

so cos 17π/6 + tan 17π/6

= -√3/2 - 1√3 , but 1/√3 = √3/3

= -√3/2 - √3/3

= ( -3√3 - 2√3)/6 = -5√3/6

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