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**1. Homework Statement**

What is the amplitude of a pendulum whose angle is given by (.10 rad)cos(5t + pi)

where t is in sec.

**2. Homework Equations**

s(t)=Acos(omega*t+phase constant)

Theta(t)=thetamax*cos(omega*t+phase constant)

**3. The Attempt at a Solution**

I'm not quite sure if I did this right:

I found the length of the string to be .392 m ( by using omega= sqrt(g/L)

So, using the small angle approximation s= .392 * sin theta where theta= the intial angle, which I found to be .1 rad by looking at the equation

s=(.392*sin(.1rad)) = .039 m

Then I used s(t) =Acos(omega*t + phase constant) with t=0

I also found omega= 5 and the phase constant is pi

.039 m = A cos(pi)

But my amplitude ends up negative. I've having a bit of trouble with positive and negative signs in SHM