need help with these questions

http://locker.palcs.org/~jbaskwill/pc/5-4practice.pdf

Question

need help with these questions

http://locker.palcs.org/~jbaskwill/pc/5-4practice.pdf

anonymous · Answer

cos x=sin 2x,
 cos x -sin 2x =0,       
cos x -(2sin x cos x=0,
cos x(1-2sin x)=0, equate to zero...
cos x=0 and 1-2sin x=0,
                     1= 2 sin x
                      1/2 = sin x
x =arc cos 0 and x= arc sin 1/2
x=pi/2          and x=pi/6

anonymous · Answer

check cos(pi/2)=sin(2xpi/2)
                 0    =     o  true
           cos(3pi/2)=sin2(3pi/2)
                      0=0  true
A ans    pi/2, 3pi/2