(sin75°+sin45°)/sin285°=
1)sin75°=sin(30°+45°)=sin30°cos45°+
sin45°cos30°=1/2*√2/2+√2/2*√3/2=
√2/4+√6/4
2)sin285°=sin(270°+15°)=-cos15°
4)sin75°+sin45°=2sin(75°+45°)/2*
cos(75°-45°)/2=2sin75°cos15°
5)2sin75°cos15°/(-cos15°)=-2sin75°=
-2(√2/4+√6/4)=-(√2/2+√6/2)=-√2/2(1+√3)