Cho hàm số y = xcosx - sinx, ta có đạo hàm là:
A. 2cosx - xsinx.
B. xsinx.
C. -xsinx.
D. Cả ba phương án đã cho đều sai.

Choose one sentence that has the closest meaning to the root one:
Unless you come on time, we will go without you.
A. Come on time or we will go without you.
B. Come on time, we will go without you.
C. Because of your punctuality, we will go without you.
D. Without your coming on time, we will go.

Cho hình chóp S.ABCD có đáy ABCD là hình chữ nhật với $AB=a\sqrt{2},BC=a$ . Cạnh bên SA vuông góc với đáy và góc giữa cạnh bên SC với đáy là 600. Tính khoảng cách từ điểm C đến mặt phẳng (SBD).
A. $\frac{{a\sqrt{{38}}}}{{29}}$     
B.   $\frac{{3a\sqrt{{58}}}}{{29}}$
C.  $\frac{{3a\sqrt{{38}}}}{{29}}$  
D.   $\frac{{3a}}{{29}}$

Cho hình chóp $\displaystyle S.ABC$ có$\displaystyle SA=SB=SC$ và tam giác$\displaystyle ABC$ vuông tại$\displaystyle B$. Vẽ$\displaystyle SH\bot \left( ABC \right)$ ,$\displaystyle H\in \left( ABC \right).$ Khẳng định nào sau đây đúng?
A. $\displaystyle H$ trùng với trung điểm của$\displaystyle AC$.
B. $\displaystyle H$ trùng với trực tâm tam giác$\displaystyle ABC.$
C. $\displaystyle H$ trùng với trọng tâm tam giác$\displaystyle ABC$.   
D. $\displaystyle H$ trùng với trung điểm của$\displaystyle BC.$

Choose one sentence that has the same meaning as the root one:
He failed the test many times, but he didn’t stop trying.
A. Failing the test never discourages him.
B. He didn't stop trying although he failed the test many times.
C. He didn’t stop trying despite his first failure.
D. He never stops trying but fails to pass the test.

Choose one sentence that has the closest meaning to the root one:
If I were taller, I could reach the top shelf.
A. I am not tall enough to reach the top shelf.
B. I am too tall to reach the top shelf.
C. I cannot reach the top shelf because I am very tall.
D. In spite of being tall, I cannot reach the top shelf.

Choose one sentence that has the same meaning as the root one:
If I had been watching the road, I wouldn’t have had an accident.
A. I have an accident because I am not watching the road.
B. I was watching the road, so I didn’t have an accident.
C. I am watching the road, so I don’t have an accident.
D. I had an accident because I wasn’t watching the road.

Choose one sentence that has the same meaning as the root one:
A very successful salesman, Mr. Smith often has more customers than he can handle.
A. Mr. Smith’s customers cannot handle him successfully.
B. Mr. Smith finds it difficult to handle his customers.
C. Mr. Smith is a successful salesman of handles to many customers.
D. Mr. Smith sometimes has too many customers to take care of.

Choose one sentence that has the same meaning as the root one:
They never made us do anything we didn’t want to do.
A. We are never made to do anything we didn't want to do.
B. We were never made to do anything we didn’t want to do.
C. We have never made to do anything we didn’t want to do.
D. We had never made to do anything we didn’t want to do.

Choose one sentence that has the same meaning as the root one:
We had planned to visit our grandmother, so we left early in the morning.
A. We left early to see our grandmother.
B. We left early because we are planning to visit our grandmother.
C. We left early because we were intending to visit our grandmother.
D. We were going to visit our grandmother so we try to leave early.