Question

2cos^{2}alpha=1+cos2alpha

Докажите тождество. 

 

 

 

 

 

 

 

Answer 1

$2cos^{2}alpha=1+cos2alpha\cos^{2}alpha-1=cos2alpha-cos^{2}alpha\-sin^2alpha=cos2alpha-cos^{2}alpha\cos^{2}alpha-sin^2alpha=cos2a\-1=cos2a\cosa=-0,5\a_1=2pi/3б2pi k\a_2=4pi/3б2pi k$