URGENT - sine graph help Can someone please answer my last question I posted. Thanks

Question:

I'm trying to graph a sine wave given different frequencies and I'm not sure how to.

Frequencies I am using: 261.625 Hz, 329.627 Hz, 391.995 Hz
I tried using the formula y(t)= sin (2πft) so the formula would be y(261.625)= sin 2π(261.625)t (using the first frequency), but it didn't work. I've seen people graph it as y= sin (261.625x)/(440) and I tried it and it works, but I don't understand how they got this formula/why to use it.