f(x) = sin(1/x)
f'(x) = -(1/х²)*cos(1/x)
f'(x) ≥ 0
-(1/х²)*cos(1/x) ≥ 0
-(1/х²)<0 при любом х≠0, поэтому cos(1/x) ≤0
π/2+2πn≤(1/x)≤3π/2+2πn; n∈Z
1/(3π/2+2πn)≤х≤1/(π/2+2πn); п∈z
