Posted by **Anonymous** on Friday, August 14, 2009 at 9:21pm.

What is the exact value of cot(5(pi)/6)?

- MATH -
**MathMate**, Friday, August 14, 2009 at 9:58pm
cot(5π/6)

= cos(5π/6) / sin(5π/6)

= sin(π/2 - 5π/6)/ cos(π/2 - 5π/6)

= sin(-π/3)/cos(-π/3)

= -sin(π/3)/cos(π/3)

= -(sqrt(3)/2)/(1/2)

= -sqrt(3)

- MATH -
**drwls**, Friday, August 14, 2009 at 10:04pm
Use Google, if you don't have a calculator. Type

tan(5*pi/6) =

in the search box.

Then take the reciprocal of that answer, for the cotangtent.

You may recognize the answer as the square root of 3.

5 pi/6 is a 150 degree angle. The reference angle is 30 degrees, but cosine is negative in the second quadrant.

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