=(tan45 degrees -tan 15 degrees) /( 1+tan45 degrees *tan 15 degrees)

=tan(45 degrees-15 degrees)

=tan30 degrees

= Sine 30 degrees/Cosine 30 degrees

= 1/2/√3/2

=√3/3

There is also method 2:

tan(A-B)=(tanA-tanB)/( 1+tanA tanB)

Tan15 = tan (45-30) = (1-√ 3/3)/(1+√ 3/3) is used to bring it back to the original equation.

So the answer is √3/3