Because the periods of sin(x) and cos(x) are both 2π, the period of each function can be obtained by dividing 2π by the coefficient of the independent variable of each function.

The period of cos(4x) is 2π/4 = π/2.

The period of cos(x/2) is 2π/( 1/2) = 4π.

The period of sin(3x+π/4) is 2π/3 = 2π/3.