Tổng của một cấp số nhân lùi vô hạn bằng $2$, tổng của ba số hạng đầu tiên của cấp số nhân bằng$\displaystyle \frac{9}{4}$. Số hạng đầu${{u}_{1}}$ của cấp số nhân đó là
A. ${{u}_{1}}=3.$ 
B. ${{u}_{1}}=4.$ 
C. ${{u}_{1}}=\frac{9}{2}.$ 
D. ${{u}_{1}}=5.$

A. -∞.
B. +∞.
C. 0.
D. Không tồn tại.

Tìm  để các hàm số  liên tục tại  
A.  
B.  
C.  
D. 1

Hàm số f(x)=x2-16x-4 khi x≠48 khi x = 4liên tục trên
A. R.
B. R\{4}.
C. (0; +∞).
D. a, b, c đều đúng.

Kết quả của giới hạn $\displaystyle \lim \frac{{{3}^{n}}-1}{{{2}^{n}}-{{2.3}^{n}}+1}$ bằng 
A. $\displaystyle -1.$ 
B. $\displaystyle -\frac{1}{2}.$ 
C. $\frac{1}{2}.$ 
D. $\displaystyle \frac{3}{2}.$

Giá trị của giới hạn $\lim \left( \sqrt{2{{n}^{2}}-n+1}-\sqrt{2{{n}^{2}}-3n+2} \right)$ là
A. $0.$ 
B. $\frac{\sqrt{2}}{2}.$ 
C. $-\infty .$ 
D. $+\infty .$

Choose the correct sentence which is built from the words and phrases given:
police / asking / man / house / break into / last night.
A. The police is asking the man having the house broken into last night.
B. The police are asking the man whose house was broken into last night.
C. The police is asking the man into whose house was broken last night.
D. The police are asking the man whose house broken into last night.

Choose the word that has the underlined part pronounced differently from the rest:
sun             sure              success            sort
A. sun            
B.  sure              
C. success            
D. sort

Choose the best answer for the following sentence:
Jim is a kind of person ____________ whom one can talk about anything.  
A. with            
B. at               
C.  to            
D. in

Choose one sentence that has the same meaning as the root one:
She is very shy; that’s why she doesn't enjoy parties. 
A. If she weren’t shy, she would enjoy parties.
B. If she isn’t very shy, she will enjoy parties.
C. If she hadn’t been too shy, she would have enjoyed parties
D. She said that if she wasn't very shy, she would enjoy parties.