# find exact values of Tan 15 degrees and Cos 75 degrees

• Apr 6th 2009, 09:01 AM
jepal
find exact values of Tan 15 degrees and Cos 75 degrees

For tan 15 degrees
Since Tan 45-tan 30=tan 15
i got this

what am i doing wrong?
• Apr 6th 2009, 09:15 AM
stapel
Quote:

Originally Posted by jepal
Since Tan 45-tan 30=tan 15

Um... not actually. The value of tan(15) is the same as the value of tan(45 - 30), but not at all the same as the value of tan(45) - tan(15)! (Surprised)

Are you familiar with function notation at all? If so, then note that the tangent function is a function, so "tan(x)" means "f(x)", where the specific name of the function "f" is "tangent". Just as f(a + b) does not mean the same thing as f(a) + f(b), so also tan(45 - 30) does not mean tan(45) - tan(30).

To simplify tan(45 - 30), you have to use the angle-difference formula they gave you. (Wink)
• Apr 6th 2009, 09:19 AM
jepal
Quote:

Originally Posted by stapel
Um... not actually. The value of tan(15) is the same as the value of tan(45 - 30), but not at all the same as the value of tan(45) - tan(15)! (Surprised)

Are you familiar with function notation at all? If so, then note that the tangent function is a function, so "tan(x)" means "f(x)", where the specific name of the function "f" is "tangent". Just as f(a + b) does not mean the same thing as f(a) + f(b), so also tan(45 - 30) does not mean tan(45) - tan(30).

To simplify tan(45 - 30), you have to use the angle-difference formula they gave you. (Wink)

Oh ok! Thank you.