Cos105°= ? tg 15° = ?

Question

Cos105°= ? tg 15° = ?

Answer 1

Cos105=cos(60+45)=cos60*cos45-sin60*sin45=1/2*√2/2-√3/2*√2/2=
=√2/2(1-√3)

tg15=tg(45-30)=(tg45-tg30)/(1+tg45*tg30)=
                          =(1-√3/3)/(1+1*√3/3)=(√3-1)/(√3+1)