Kako izražate cos (4theta) v smislu cos (2theta)?

Kako izražate cos (4theta) v smislu cos (2theta)?
Anonim

Odgovor:

#cos (4theta) = 2 (cos (2theta)) ^ 2-1 #

Pojasnilo:

Začnite z zamenjavo # 4theta # z # 2 theta + 2theta #

#cos (4theta) = cos (2theta + 2theta) #

To vem #cos (a + b) = cos (a) cos (b) -sin (a) sin (b) # potem

#cos (2theta + 2theta) = (cos (2theta)) ^ 2- (sin (2theta)) ^ 2 #

To vem # (cos (x)) ^ 2+ (sin (x)) ^ 2 = 1 # potem

# (sin (x)) ^ 2 = 1- (cos (x)) ^ 2 #

#rarr cos (4theta) = (cos (2theta)) ^ 2- (1- (cos (2theta)) ^ 2) #

# = 2 (cos (2theta)) ^ 2-1 #