80 + 90
Giúp mik nha
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NL
Tìm a,b biết:
a) a/b=1/-3 và a-2b=14
b) 2/9.3^a+1-4.3^a=-90
Giúp mik với pleaseee!!!! Cảm ơn nhìu ak <3
1
4 tháng 11 2021
a: Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{a}{1}=\dfrac{b}{-3}=\dfrac{a-2b}{1-2\cdot\left(-3\right)}=\dfrac{14}{7}=2\)
Do đó: a=2; b=-6
NT
1
VD
18 tháng 3 2022
\(B=\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}\\ =\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}+\dfrac{1}{7\times8}+\dfrac{1}{8\times9}+\dfrac{1}{9\times10}\\ =\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\\ =\dfrac{1}{4}-\dfrac{1}{10}\\ =\dfrac{10}{40}-\dfrac{4}{40}\\ =\dfrac{6}{40}\\ =\dfrac{3}{20}\)
Q
25 tháng 7 2021
A 30 độ
tia tới hợp vs gương 75 độ nên tia tới là 90-75=15 độ
tia phản xạ bằng tia tới nên bằng 15 độ
hai tia hợp lại 15+15=30 độ
25 tháng 7 2021
Nếu tia sáng tới hợp với gương phẳng một góc 750 thì góc tới là:
\(i=90^0-75^0=15^0\)
Tia phản xạ hợp với tia tới một góc: α = \(2i=30^{0^{ }}\)
6 tháng 6 2016
like living in the countryside because of some reasons. Environmentally speaking, it is a peaceful place. The air is fresh. The space is quiet. We can enjoy healthy natural conditions without
worrying much about environmental pollution.
As for social security, the countryside is a safer place than a city. While urban security situation is always complicated with all kinds of crimes, rural areas are much more secure because most of countrymen are friendly and ready to help one another.
Moreover, rural life is also easier that in cities. People in cities are easy to get stressed because of pollution, job pressures, competitions, etc ... On the contrary, those bad things
are very rare in the countryside. To sum up, except income matters, the countryside is a better residence than cities.
That was my thought, hope you like it !!^_^
6 tháng 6 2016
I like living in the country because of some reasons.In the countryside, the air is clean, the water is pure and the environment is beautiful while most cities choke in their own filth and pollution. Also, people there are friendly. A friendly smile while passing is standard in the countryside and it’s sincere; whereas, in the city few people smile at you. In fact, they are likely to regard you with suspicion if you smile at them. Besides, people in the countryside enjoy more tranquillity than those in big cities. There is less noise and life is calm and relaxed. Once on foot in the city, you find yourself in an ant colony, or a cage with too many rats. As for food, it is fresher in the countryside. Farmers sell fresh produce, which they bring straight from the fields, at their stand just around the corner. Moreover, the city is rife with violence and crimes: Many thefts and murders often take place in the city.
That's all my thought.I hope you like it!
VT
2
12 tháng 6 2020
\(29-\left(\frac{209}{10}x-80\right)=0\)
\(\Leftrightarrow\frac{209}{10}x-80=29\)
\(\Leftrightarrow\frac{209}{10}x=109\Leftrightarrow x=\frac{1090}{209}\)
PP
2
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
4 tháng 5 2023
Số đó là: 640 \(\times\) 80:100 = 512
\(\dfrac{2}{5}\) số đó là: 512 \(\times\) \(\dfrac{2}{5}\) = 204,8
20 tháng 4 2018
Nowadays, energy is being run out more and more so it is one of the most important things of our life. We need to save energy because nobody of us can lives without energy. So why don't we start to do it right in our home? We have many ways to save energy in our home. One of those ways is using electricity, water and gas economically. Such as we should turn off the light in room when we go out or in unnecessary situations, avoid wasting water, shut the kitchen stove when stop cooking. Use a microwave instead of a stove to reheat food. Use rechargeable batteries instead of disposable batteries... Besides, we should use electrical equipments which are energy - saving. Such as using lights and fans that have low capacity, or using equipments which reserve electricty. Not only do these help us to save money but also they work effectively.
In addition, we should frequently check electrical equipments in our home in order to fix opportunely. In summary, we need to save energy so that energy isn't run out and continues to serve human's life.
TN
20 tháng 4 2018
Nowadays, energy is necessary for our life. There are many kind of energy : ocean energy, electric energy, solar energy, wind energy... But energy also limit , so we must save energy. We can make some following ways.
To save petrol energy, we should:
+ Limit travel by car, motorbike, train...
You can using bicycles or walk.This not only help you save energy but also avoid traffic jams and can save your money any more.
- To save electricity energy, we should:
+ Turn off the light , the fans, the air-conditioner, you should close it after using.Avoid ironning close at peak hours...
+ When buying somethings, we should choose devices with costly a low electricity.
There are many ways to save water:
+ Turn off the faucet after using it
+ Don't let children play with water, if you let chidren play with water , this ill a lot of water.
- In the kitchen we should save gas energy by many ways:
+ turn off gas after cooking
+ don't use gas too much
+ when the food ripe, we should turn off gas immidiately to save gas.
- saving energy is our duty.
If you follow ways above, you can not only save energy but also save money very much and protect the environment.
80 +90 = 170 nha
TK MK NHA MK NHANH NHÂT NEK
Số cần tìm là :
80 + 90 = 170
Đáp số : .......