
Average Velocity
The displacement (in centimeters) of a particle moving back and forth along a straight line is given by the equation of motion s = 2sin(πt) + 4cos(πt), where t is measured in seconds. (Round all answers to the nearest hundredth.)
Find the Average velocity from time [1,2], [1,1.1], [1,1.01], [1,1.001], and approximate the instantaneous velocity for t=1
I tried (for the first one) doing (s(2)s(1))/(21), but I'm not getting the right answer. Once I round to the nearest hundredth, I get 0.09 and the online grading program says that is wrong. I've tried the same formula for all the others and they're all wrong. I'm obviously not setting this up correctly. Any ideas?
Thanks for your help.

[s(2)s(1)]/(21)
= s(2) s(1)
= 2sin(2pi) + 4cos(2pi)  2sin(pi)  4cos(pi)
= 4  (4)
= 8

ok, for some reason my calculator is giving weird results when I use trig functions. I got all of them except for the instantaneous velocity one. When t=1. I plugged t=1 into 2sin(Pi*t)+4cos(Pi*t) and I got 4. The online program said that was wrong.
EDIT:
Never mind, I just got it.