HOC24
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Bài học
Rót H 2 S O 4 đặc vào cốc đựng chất A màu trắng thấy A dần dần chuyển sang màu vàng, sau đó chuyển sang màu nâu và cuối cùng thành một khối đen xốp, bị bọt khí đẩy lên miệng cốc. A là chất nào trong các chất sau
A. NaCl
B. C O 2 rắn
C. Saccarozơ
D. C u S O 4 khan
Read the passage and answer the questions.
Energy is one of the problems that many people are interested in. It is not an unfamiliar word. It is heard, said, discussed day after day. It is close to everyone’s daily life. You turn on a lamp and it is energy that gives you light. You turn on a TV and it is energy that gives you pictures and sound. You ride a motorcycle and it is energy that gives you movement. You cook your meals and it is energy that gives you heat to boil rice.
The problem is that the demand for energy is rising and that the price of energy is getting higher and higher. The supply of energy on earth is limited. It cannot provide us forever. The shortage of energy in the future is inevitable. Therefore, saving energy is a must if we want to continue to live in a safe and sound world.
* Notice:
familiar: thân thuộc
demand: nhu cầu
inevitable: chắc chắn xảy ra
Question: How is the price of energy nowadays?
→………………………………………………………………………………………….
Cho cos x = 3 5 , ( π 2 < x < π )
Tính giá trị biểu thức sau:
P = cos 2 x - 1 2 sin 2 x