Anyone have any idea how to do this?

 

Hint- Any time you use sin and cos, your are actually doing a conversion between Cartesian (linear) and polar (non-linear) coordinate systems. One way or the other, depending on which way you are going, which alters the resulting magnitude...

 

Hint #2: 't' is time, and because they ask the question regarding 100kHz, you know the kHz is per second, so 't' is in terms of seconds or sub-seconds (like miliseconds).

What happens if you do the equation with 't' as 0.100, then 0.200, then 0.300, etc until you get to 1 second?

 

Hint #3
The formula of a cosine wave at frequency f is given as
v = Acos(2πft)

If the equation is v = cos(1000 * 2πt)
what is the equation in terms of f if f = 100kHz?

 

\[\cases{cos\ φ=sin\left({φ+\frac \pi 2}\right)\\sin\ φ=cos\left({φ-\frac \pi 2}\right)\\sin\ \alpha±sin\ \beta=2·sin\frac{\alpha±\beta}2·cos\frac{\alpha∓\beta}2\\cos\ \alpha±cos\ \beta=±2·{}^{cos}_{sin}\frac{\alpha+\beta}2·{}^{cos}_{sin}\frac{\alpha-\beta}2}\]
also (likely more relevant for your case)
\[sin^2\alpha=\frac{1-cos\left(2·\alpha\right)}2\\ cos^2\alpha=\frac{cos\left(2·\alpha\right)+1}2\]
while
\[Def.:\ \alpha=2\pi\text{f}·t\ \rightarrow\ 2\alpha=2\pi\left({2\text{f}}\right)·t\]

 

Thank you very much with all your help, wow, the answer is already in front of me. Thanks again!