Is the Highlighted Portion a Mistake and Where Does the PI Go?

[Turion]

The highlighted in yellow is a mistake, right? I might be going insane.

Where does the PI go?

 

[Office_Shredder]

$$\cos(4(t+\pi)) = \cos(4t+4\pi) = \cos(4t)$$

 

[SteamKing]

Remember, sin and cos are periodic functions with period 2k*pi, k = integer.

 

[Turion]

@Office_Shredder: Opps. Nice catch.

@SteamKing: Isn't the period 2pi/k where k is the coefficient of t?

 

[blue_raver22]

I cannot determine if the highlighted portion is a mistake or not without additional context. It is important to carefully review all data and information before making any conclusions. As for the location of the PI, it is unclear what you are referring to. Can you please provide more information?