1.) sin3x = -√2/2
3x = (-1)^n+1 * arcsin√2/2 + pi*n
3x = (-1)^n+1 * pi/4 + pi*n
x = (-1)^n+1 * pi/12 + pi*n/3
2.) cos(x/5) = -√3/2
x/5 = +-arccos√3/2 + 2pi*n
x = +-5pi/6 + 10pi*n
3.) tg(2x - pi/3) =1
2x - pi/3 = arctg1 + pi*n
2x = pi/4 + pi/3 + pi*n
2x = 7pi/12 + pi*n
x = 7pi/24 + pi*n/2