sin (-15º) cos75º+cos15ºsin75º=

sin (-15) cos (60+15)+cos15sin (60+15)=cos15 (sin60cos15+cos60sin15) -sin15 (cos60cos15-sin60sin15)=sin60 (cos15) ^2+cos60cos15sin15-cos60cos15sin15+sin60 (sin15) ^2=sin60 (cos15) ^2+(sin15) ^2)+cos60 (cos15sin15-cos15sin15)=sin60=(корень из 3) /2