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