SOLUTION: What is the exact value of tan 105 degrees? I did the work but find myself lost on what I was doing in showing the work. Here's what I got. tan(45+60) so then I used a sum diffe

Algebra ->  Trigonometry-basics -> SOLUTION: What is the exact value of tan 105 degrees? I did the work but find myself lost on what I was doing in showing the work. Here's what I got. tan(45+60) so then I used a sum diffe      Log On


   

Question 807653: What is the exact value of tan 105 degrees? I did the work but find myself lost on what I was doing in showing the work. Here's what I got.
tan(45+60)
so then I used a sum difference formula
=tan(45)tan(60)/(1-tan(45)tan60) The top I got radical 3 plus 1 and bottom is -radical 3 plus 1 I tried on the calculator but it gave me negative(-) radical 3 minus 1 divided by 2. What did I do wrong?
Answer by fcabanski(1391) About Me  (Show Source):
You can put this solution on YOUR website!
tan(x+y) does not = tan(45)tan(60)/(1-tan(45)tan(60)


The identity is tan(x+y) = (tan(x) + tan(y))/(1-tan(x)tan(y))


You multiplied instead of added (in the numerator).