Để phương trình $\displaystyle \frac{{{\sin }^{6}}x+{{\cos }^{6}}x}{\tan \left( x+\frac{\pi }{4} \right)\tan \left( x-\frac{\pi }{4} \right)}=m$ có nghiệm, tham số m phải thỏa mãn điều kiện:
A. $\displaystyle -2\le m\le -1$ 
B. $\displaystyle -1\le m\le -\frac{1}{4}$ 
C. $\displaystyle 1\le m\le 2$ 
D. $\displaystyle \frac{1}{4}\le m\le 1$

Choose the best answer for the following sentence:
''Ruth is a surgeon, isn’t she?”
"Yes, but her family doesn’t approve _________ her career.”  
A. from  
B. of  
C. about  
D. with

Choose the best answer for the following sentence:
_______________ water or air does not move and often smells bad. 
A. Stagnant                   
B. Stagnated                   
C. Stagnation                    
D. Stagnating

Choose the best answer for the following sentence:
Water polo is a team water game, with six field players and one goalie in each team. The winner of the game is the team that scores more ____________.
 
A. nets                   
B. goals                
C. plays                   
D. balls

Choose the best answer for the following sentence:
 "How dark your sister’s hair is!'' '' It's _____________ mine when I was ay her age.'' 
A. no darker than
B. no more darker than
C. no dark more than
D. not dark as

Giải phương trình $cos\frac{4x}{3}=co{{s}^{2}}x$. 
A. $\left[ \begin{array}{l}x=k3\pi \\x=\pm \frac{\pi }{4}+k3\pi \\x=\pm \frac{5\pi }{4}+k3\pi \end{array} \right.$ 
B. $\left[ \begin{array}{l}x=k\pi \\x=\pm \frac{\pi }{4}+k\pi \\x=\pm \frac{5\pi }{4}+k\pi \end{array} \right.$ 
C. $\left[ \begin{array}{l}x=k3\pi \\x=\pm \frac{\pi }{4}+k3\pi \end{array} \right.$ 
D. $\left[ \begin{array}{l}x=k3\pi \\x=\pm \frac{5\pi }{4}+k3\pi \end{array} \right.$

Tập nghiệm của phương trình cosx = 2|cosx| + 5 là
A. .
B. .
C. .
D. Ø.

Điều kiện xác định của hàm số $y=\frac{2\sin x+1}{1-\cos x}$ là
A. $x
e k2\pi ,k\in Z.$
B. $x
e k\pi ,k\in Z.$
C. $x
e \frac{\pi }{2}+k\pi ,k\in Z.$
D. $x
e \frac{\pi }{2}+k2\pi ,k\in Z.$

A. -∞.
B. +∞.
C. 4.
D. 6.

A. D = e.
B. D = e2.
C. .
D. D = +∞.