Then the period of sin2/3x is 2 pie /(2/3).

=3 pai

(2)cosx period was divided into two schools.

Y= 1/2cos4x period

=2 Pie chart /4

= Pai /2

The (1) function is the same as the sinx monotone interval.

The added interval is [2k Pie Chart-Pie Chart /2, 2k Pie Chart+Pie Chart /2]

The subtraction interval is [2k pie+pie /2, 2k pie +3 pie /2], where k is an integer.

(2)y=-cosx, and the increase and decrease interval is opposite to cosx.

The range of increase is [2k school+school, 2k school +2 school]

Subtract the interval [2k pie, 2k pie+pie], and k is an integer.