sin(50度)*cos(10度)+sin(40度)*sin(10度)=

sin(50度)*cos(10度)+sin(40度)*sin(10度)
=sin(50度)*cos(10度)+sin(90度-50度)sin(10度)
=sin(50度)*cos(10度)+cos(50度)sin(10度)
=sin(50度+10度)
=sin60度
=√3/2