1,5 A) 22 COS 2 0 COSX + =  X = − 2 3 3 = +  = − + 0,5 2...

Câu 1 1,5

a) ₂

2 cos 2 0 cos

x + =  x = − 2

3 3

 = +  = − + 0,5

2 2

x  k  x  k 

4 4

b) 3 1 3

3 sin 2 os2x= 3 sin 2 cos 2

x + c  x + x =

2 2 2

0,25

 

   +   =

sin 2 sin

x  

6 3

    

 + = +  = +

x k x k

 

6 3 12

   

 + = +  = +

 



6 3 2

c) cos 3 .cos x

x + sin 3 .sin x

x = cos 4

x

 + =

x x x x x x x

cos 3 .cos .cos sin 3 .sin .sin cos 4

1 1

( ) ( )

 + − − =

cos 4 cos 2 .cos cos 4 cos 2 .sin cos 4

( )

1 cos 4 x .(cos sin ) cos 2 . cos sin cos 4

 

  − + +  =

x x x x x x

2

1 cos 2 . 1 cos 4 cos 4

( )

x x x

 =

x x

cos 2 cos 4

cos 4 cos 2

 

 =

x k

   =



 = 