- Joined
- Jun 27, 2021
- Messages
- 5,386
- Reaction score
- 422
Section 5.4
I need help with 87 and 89.
I need help with 87 and 89.
87.
cos(n*pi+theta)=(-1)^n*cos(theta) , n is an integer
when n is even number, n=2k, k element Z
then cos(n*pi+theta)=cos(2k*pi+theta)=1^(2k)*cos(theta)=cos(theta)
then cos(n*pi+theta)=cos((2k+1)*pi+theta)=(-1^(2k)cos(theta)=- cos(theta)
cos(n*pi+theta)=(-1)^n*cos(theta)-> proven
89. is just as previous post