Given cos (2pi / 5) = (sqrt (5) -1) / 4, ano ang cos (3pi / 5)?

Given cos (2pi / 5) = (sqrt (5) -1) / 4, ano ang cos (3pi / 5)?
Anonim

Sagot:

# (1-sqrt (5)) / 4 #

Paliwanag:

#cos (theta) = -cos (pi-theta) #

samakatuwid

#cos (3pi / 5) = cos (pi-2pi / 5) = - cos (2pi / 5) #

# = (1-sqrt (5)) / 4 #

Sagot:

# = - (sqrt5-1) / 4 #

Paliwanag:

#cos ((3pi) / 5) = cos (pi- (2pi) / 5) = - cos ((2pi) / 5) = - (sqrt5-1) / 4 #