Question

sa see calculeze cos (x+30)cos60-x)-sin (x+30)sin(60-x)

Answer 1

Stim formula generala
$\cos{(a+b)}=\cos{a}\cos{b}-\sin{a}\sin{b}$ Daca inlocuim a cu x+30 si b cu 60-x obtinem exact relatia ta
$<span>\cos{x+30}\cos{60-x}-\sin{x+30}\sin{60-x}=\cos{x+30+60-x}=\cos{90}=0</span>$