Các số có tổng các chữ số chia hết cho 9 thì chia hết cho 9 và chỉ những số đó mới chia hết cho 9. 

-1/27 .5/9 nhe

(\(\dfrac{3}{7}\)+(\(-\dfrac{3}{7}\))). \(\left(-\dfrac{1}{27}\right)\).\(\dfrac{5}{9}\)

= 0.\(\left(-\dfrac{1}{27}\right)\).​\(\dfrac{5}{9}\)

=0

1+2+3+4+...+50 x 2x = 2624

1275 x 2x = 2624 

2x = 2624 :1275

2x = 2624/1275

x = 2624/1275 : 2

x = 1312/1275

S=\(\dfrac{127}{128}\)

khom có đk

What is Air Pollution?
Air pollution is a major change in air composition, caused by smoke, dust, water vapor or strange gases entering the air, causing strange odors, reduced visibility and climate change. They directly affect the health of humans as well as animals and plants on earth.
Current status of air pollution in Vietnam
Air pollution is a serious problem in the world and Vietnam is no exception. According to the annual report on the environmental performance index (EPI) conducted by the US Environmental Organization, Vietnam is one of the 10 countries with the highest air pollution levels in Asia.
 Current status of air pollution in the world
According to the 2020 State of the Global Air Report released by the Health Effects Institute (HEI) and the Institute for Health Metrics and Evaluation (IHME) at the University of Washington and the University of British Columbia on October 21, Air pollution in the world is very alarming. 
Air pollution is threatening human life 
The causes of air pollution come from many sources, there are basically two main causes: man-made and natural.
Natural causes
There are many natural causes such as volcanic eruptions, tsunamis, etc. that also pollute the air
Causes from humans (man-made)
There are many man-made causes from daily activities and agricultural production activities. Not only Vietnam but many developing countries are also experiencing this situation. Smoke and dust from exhaust pipes of factories and plants in industrial zones darken the sky. They emit CO2, CO, SO2, NOx and some other organic substances at extremely high concentrations.

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