cos(260)*sin(260)=sin(520)/2=sin(160)/2;
sin(160)*cos(160)/2=sin(320)/4=-sin(40)/4;
sin130=sin50=cos40;
-sin40/4*cos40=-sin(80)/8
cos(260)*sin(260)=sin(520)/2=sin(160)/2;
sin(160)*cos(160)/2=sin(320)/4=-sin(40)/4;
sin130=sin50=cos40;
-sin40/4*cos40=-sin(80)/8