solve the equation on the interval 0
solve the equation on the interval 0<_<2
sec(3\\2)=-2
Solution
sec(3x/2) = -2
cos(3x/2) = -1/2
3x/2 = cos^-1(-1/2)
3x/2 = 2k*pi +2pi/3
x = ( 4pi +12k*pi)/9
3x/2 = 2k*pi +4pi/3
x = (8pi +12k*pi)/9
Plug k= 0, 1, 2....
x = 4pi/9 , 8pi/9 , 16pi/9 ; 0<=x<= 2pi
