Hello,

to #3.a)

(For some reason the Latex doesn't work properly anymore. I'll repeat the equations in plain text)

cos(2x) = 0 or cos(2x) = -1 or cos(2x) = 1

This character π means pi

From the 1rst equ.:

2x = -π/2 --> x = -π/4 or

2x = -3π/2 ---> x = -3π/4

from the 2nd equ.:

2x = -π ---> x = -π/2

from the 3rd equ.:

2x = 0 ---> x = 0 or

2x = -2π ---> x = -π

EB