Explicație pas cu pas:
trebuie sa il scriem pe 1920 in 360x+a
1920:360=5 r 120
adica cos(360×5+120)=cos(360×5)sin120+cos120sin(360×5)=cos120=cos(180-120)*=cos60=1/2
cos360 fiind 0
la fel si la tg2040
2040:180=5 rest 240
tg2040=tg(5*360+240)=sin(5×360+240)/cos(5x360+240)=[sin(5×360)cos240+sin240cos(5×360)]/[cos(5×360)cos240-sin(5×360)cos240]=cos240/-cos240=-1
cos1920+tg2040=1/2-1=0.5-1=-0.5=-1/2
