No this has nothing to do with Galileo's Law it is a completely different
What stays the same is the definition of average velocity it is still
[s(t2) - s(t1)]/(t2-t1)
s = 5sin(πt) + 2cos(πt
Compute [s(2) -s(1)]/[2-1]
The instantaneous velocity is the derivative but as you've been asked for
an approximation I'm assuming you haven't done derivatives yet?
Compute [s(1.01) -s(1)]/[1.01-1]