Can you solve the word problem from hell!? See below for details. Special thanks to all who reply :D?

Question

An oscilloscope hooked up to an AC circuit, shows a sine curve on the display. The device records the current in amperes (symbol A) on the vertical axis and time in seconds on the horizontal axis. At t=1/120s the current reads a minimum value of -4.5A. At t=60s the current reads its maximum value of 4.5A. Determine the equation of the function
that expresses the current in relation to time. What is the current after 4.0s?

I made a little mistake where it says 60s it is suppose to say 1/60s, my bad, sorry.

Answer 1

I believe it should be at t = 1/60 s, the current reads its maximum value.
Therefore, the equation is
I(t) = 4.5sin(120pi t - 3pi/2)
I(4.0) = 4.5

Answer 2

Let/s assume A = 4.5A when t = 1/60 s
P = 2(1/60 - 1/120) = 1/60, f = 120π
A = 4.5cos(120πt)

Answer 3

i did this in radians.

sine curve ===> y = amp sin(b(x-c)) + d

t= 1/120 ===> y = -4.5
t = 60 ====> y = 4.5
phase shift 1/120 minus one-fourth period
half of period is 60 - 1/120 period = 2pi/b
2pi/b = 120 - 1/60 ===> b=2pi / (120-1/60) ==> b=.05237
c = 1/120 - 30 + 1/240 = -29.9875
are you sure you have numbers right? not too nice...

y = -4.5 sin [0.052367(x+29.9875)]
plug in 4
y = -4.5 sin [0.052367(4+29.9875)] = -4.402A
:)