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

1. ## 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?

2. 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)!

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.

3. 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)!

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.
Oh ok! Thank you.