sin 7π/12=sin (4π/12+3π/12)= sin(π/3+π/4)=sinπ/3cosπ/4+sinπ/4cosπ/3=
(√3/2 +1/2)* √2/2=
=(√6+√2)/4
cos 7π/12= -√(1-sin²7π/12)
sau
cos 7π/12= cosπ/3cosπ/4-sinπ/3sinπ/4=(√2/2) * (1/2-√3/2)= (√2-√6)/4
sin11π/12=sin(π-11/12) =sinπ/12= sin (π/3-π/4)=
sinπ/3*cosπ/4-sinπ/4*cosπ/3=(√3/2 -1/2)* √2/2
(√6-√2)/4
cos 11π/12= -cos(π-π/12)=-cosπ/12 =-cos(π/3-π/4)
-(cosπ/3cosπ/4+sinπ/3sinπ/4)= -(√3/2+1/2) *(√2/2)=-(√6+√2)/2
