sin15°cos15°+cos15°sin105°
=(sin30°)/2+cos15°sin75°
=1/4+cos15°cos15°
=1/4+(cos15°)^2
因为cos30°=2(cos15°)^2 -1
所以
(cos15°)^2=[cos30°+1]/2=(√3+2)/4
sin15°cos15°+cos15°sin105°
=1/4+(√3+2)/4
=(√3+3)/4