pls help me!

The displacement (in centimeters) of a particle moving back and forth along a straight line is given by the equation of motion 

s = 5 sin(πt) + 2 cos(πt),

 where t is measured in seconds. (Round your answers to two decimal places.)

$s = 5 sin(\pi t) + 2 cos(\pi t)\\ \frac{ds}{dt}=v(t)=5\pi cos(\pi t)-2\pi sin(\pi t)$

a) Find the average velocity during each time period.

(i)    [1, 2]  cm/s     

$s(t) = 5 sin(\pi t) + 2 cos(\pi t)\\ s(1) = 5 sin(\pi ) + 2 cos(\pi )=-2\\ s(2) = 5 sin(2\pi ) + 2 cos(2\pi )=0+2=2\\ Average\;\; velocity = \frac{2--2}{2-1} =4cm/sec$

(ii)    [1, 1.1]  cm/s 

(iii)    [1, 1.01]  cm/s 

(iv)    [1, 1.001]  cm/s 

(b) Estimate the instantaneous velocity of the particle when t = 1. 
 cm/s

$v(1)=5\pi cos(\pi )-2\pi sin(\pi )=-5\pi-0=-5\pi\;cm/sec$

You can do the others yourself :)