sin40+sin50=
=sin(45-5)+sin(45+5)=
=sin45*cos5-sin5*cos45 +sin45*cos5+sin5*cos45=<сокращаем sin5*cos45
=2sin45*cos5 <произведение
sin40+sin50=
=sin(45-5)+sin(45+5)=
=sin45*cos5-sin5*cos45 +sin45*cos5+sin5*cos45=<сокращаем sin5*cos45
=2sin45*cos5 <произведение