An oscillator has an amplitude of 3.2. At this instant the displacement of the oscillator is 1.4. What are the two possible phases of the oscillator at this instant?

so i used the equation x=A cos (omega(t) + phase zero)

which looks like
1.4=3.2 cos phase
.4375=cos phase
so than i take
cos^-1 of .4375 to get the phase..is this right?

3 answers

That looks good.
Remmeber there will be two phases that have a positive cosine value.
how do i figure that out?
arccos(0.4375)=+-1.118 radians.

cos(-1.118 radians) = cos( (2*pi) - 1.118 )
=cos(5.1652 radians)

either of these will give a cosine value of +0.4375