Answer
$phase = -0.64$
Work Step by Step
If C is any real number and $B> 0$, then the graphs of
$y = A\sin(Bx+C)$ and $y = A\cos (Bx+C)$ will have
$Period = \frac{2\pi}{B}$
$Phase = C$
$Horizontal\ shift = –\frac{C}{B}$
so in equation $y = 2\cos (990t - 0.64)$
b) So here $phase = -0.64$
$Horizontal\ shift = –\frac{-0.64}{990} = 0.0006464$
$Period = \frac{2\pi}{990} = 0.006343$
So one cycle will start from $x = 0.000646$
and will go upto $x = 0.000646 + 0.006343 = 0.006989$
