Using the derivative or graph of the chosen pair of frequencies (in this case f1=10 , f2=8) determine 3 occasions (values of x) when it is stationary(not moving).

So derivative is -18cos(x)sin(9x)-2sin(x)cos(9x)

2nd derivative is (if any help) 36sin(x)sin(9x)-164cos(x)cos(9x)

graph of function will be attached.

then verify that the times are accurate by making appropriate substitutions and calculations.

plz help and explain steps done.