The qustion asks find all solutiions in the interval [0,2pie), correct to five decomal places.
5 cos 2x= 2
let p = 2x
cos p = 2/5
all values between p = 0 and p = 4 pi
because p is twice x
cos^-1 .4 = 1.2 approx, you do the five decimals
that is in the first quadrant.
to get the value in the fourth quadrant do 2 pi - 1.2
that is all the p between 0 and 2 pi but we need to go around to 4 pi so
add 2 pi to each of them for the second time around the circle
now divide all those four values of p by 2 to get values of x