3) sin50cos20 + cos50sin70-------------------------------------=sin120cos20 + cos120sin704) cos30cos60 - sin30sin70--------------------------------------=cos90cos60 - sin90sin70
3) sin50cos20 + cos50sin70-------------------------------------=sin120cos20 + cos120sin704) cos30cos60 - sin30sin70--------------------------------------=cos90cos60 - sin90sin70