Cho khối chóp S . A B C  có đáy là tam giác vuông tại A, S B ⊥ A B C ,   A B = a ,   A C B ^ = 30 ° ,  góc giữa đường thẳng SC và mặt phẳng (ABC) là 60 ° .  Tính thể tích V của khối chóp theo a.

A.  V = 3 a 3

B.  V = a 3

C.  V = 2 a 3

D.  V = 3 a 3 2

Tập nghiệm của phương trình  5 + 2 x = 3 x - 2  là

A.  7

B.  - 3 5

C.  7 ; - 3 5

D. tập hợp có nhiều hơn hai

Everyone is aware of how important water is to the existence of our green planet, and every living thing that grows as diverse as today begins to grow and develop. that school is water. Today, water is a life-sustaining component and indispensable for all living organisms on earth: plants, animals, and humans.
- I know that there are two main causes (or two main sources) that affect the water source: ecosystems in the water environment and external factors including: human and many other aggregates Impact on (not yourself). The fact that everyone knows very well is the most polluted source of water, stemming from the second factor I mentioned above in which humans are the primary and most active agents. Negative to the water source, specifically:
+ Directly: all daily-life wastes, medical wastes, etc., if not treated, are dumped into water sources, industrial wastes account for large quantities of toxic substances affecting water sources. industry, ... most of the river. Everything that I have just said is done by people (factories, factories, ... where is it all created by man), there are many problems to mention if you need to speak very It is long and even the whole year is not finished, I just talk about the problems in the society today.
+ Indirectly: human impacts on nature such as deforestation, the air emissions into the air change negatively to the natural-climatic conditions ..., the consequences of the long-term process is the Earth's warming, climate change on the earth -> greatly affects the Earth's ecosystems including humans, altering air-conditioning, altering the flow of climate. And the flow of water affects all the ecosystems living in those environments.

3dam² 15m² bằng bao nhiêu dam² ?

A. 315dam²

B. 3,15dam².

C. 3150 dam².

D.3015dam²