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June 19, 2013

# Homework Help: math

Posted by lily on Friday, April 10, 2009 at 1:34am.

use the sum or difference identify to find the exact vlue of tan 105 degree.my ans.sqrt plus (3) plus 1 . wrong so can you correct it for me please thank you .

• math - Damon, Friday, April 10, 2009 at 2:25am

105 = 45 +60
tan 45 = 1
tan 60 = sqrt 3
tan(a+b) = (tan a+tan b)/(1-tan a tanb)
=(1+sqrt 3)/(1-sqrt 3)
= (1+sqrt3)(1+sqrt 3)/[(1-sqrt 3)(1+sqrt 3)]
= (4+2sqrt3)/(1-3)
= -(2 + sqrt 3)

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