Question

ctg α - sin 2 α = ctg α cos 2 α

Доведіть тотожність.

Answer 1

ctga-sin2a=cosa/sina - 2*sina*cosa= (cosa-2sin²a*cosa)/sina=cosa(1-2sin²a)/sina=

=ctga*(1-2sin²a)=ctga*cos2a

 

 

Answer 2

ctga-sin2a=cosa/sina - 2*sina*cosa= (cosa-2sin²a*cosa)/sina=cosa(1-2sin²a)/sina=

=ctga*(1-2sin²a)=ctga*cos2a