Răspuns:
Cos(x-y)= cosxcosy+sinxsiny
Cos(x+y)= cosxcosy-sinxsiny
Cos(m-n)= cosmcosn+sinmsinn
Cos(m+n)= cosmcosn-sinmsinn
Cos(p-q)= cospcosq+sinpsinq
Cos(p+q)= cospcosq-sinpsinq
Cos 2y=cos^2y-sin^2y
=2cos^2y-1
Cos 2alfa==cos^2alfa-sin^2alfa
=2cos^2alfa-1
Cos 2beta==cos^2beta-sin^2ybeta
=2cos^2beta-1
Explicație pas cu pas: