4*sin(x) = 3*cos(x)
<=> tan(x) = 3/4
we have divided by cos(x), so we have to verify that it's well defined, the values of x that can cause problems are x = pi/2 + pi*k, (k is an integer)
the equation obviously doesn't hold in this set of points so we're ok.
now as you have already seen in part 1 the tan function is periodic with a period of pi, thus the equation also true for:
tan(x + pi*k) = 3/4
<=> x+pi*k = atan(3/4)
<=> x = atan(3/4) + pi*k
now choose the values in the given range namely (0 <= x <= 2*pi)...