(1-1/120)*(1-1/140)*...*(1-1/2014)
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1 tháng 8 2016
câu b )
ta phân phối 2 vô
=> \(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+\frac{2}{17.19}+\frac{x}{209}=\frac{10}{209}\)
\(\Rightarrow\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{17}-\frac{1}{19}+\frac{x}{209}=\frac{10}{209}\)
\(\Rightarrow\frac{8}{209}+\frac{x}{209}=\frac{10}{209}\)
\(\Rightarrow\frac{x}{209}=\frac{2}{209}\)
\(\Rightarrow x=2\)
CL
6
AL
8 tháng 5 2021
4.There are many types of natural disasters, storms are one of them, a storm is a turbulent state in the atmosphere and a type of extreme weather.There are many types of storms: Snowstorms: a very heavy snow phenomenon. thick with strong winds. Usually occurs in cold or temperate countries. Sand tornado: also known as sand demon, is a phenomenon of sand swept up very high, occurring at noon in desert areas. To: is the phenomenon of wind speeding up suddenly, accompanied by strong thunderstorms. Thunderstorms: are storms accompanied by thunder, heavy rain or hail. Tornado: is a phenomenon of a circular swirling air stream extending from a thunderstorm cloud down to the ground, especially in that a thunderstorm can descend on empty fields (rural areas) and cities. Fire storm: is a way to call intense fires that have created their own convection system and wind, making it extremely large and difficult to control or extinguish. Tropical cyclones are rapidly rotating storm systems characterized by a center of low pressure, strong winds and a spiral cloud structure that produces heavy rain. lots of homes. The bigger the storm, the more loss of life and property. Storms often break trees and damage homes. A hurricane with a tornado can sweep people and houses away, break trees, cause crop damage, and cause accidents to planes and boats. Therefore, we must take timely measures to prevent storms, we must resist our house carefully, so we can prevent a little hảm from storm.
AL
8 tháng 5 2021
5. To protect the environment, in my opinion, I should start with the small things that are closest to us. For example saving electricity: turn off the TV when not watching; Or do not forget to turn off the lights when going out, replacing more energy-efficient devices. Saving water: reusing water as vegetable wash instead of discarding it, you can water the plants in the garden; When washing dishes, wash in a basin, do not wash directly under running water for too long. Along with saving is keeping general hygiene. This is very important. To keep clean is to dispose of garbage in the right place; not cutting flowers to break branches destroying nature; not graffiti on the wall; When you see garbage falling on the street, you will pick it up and put it in the trash; is to plant some more trees in front of the house, etc. These everyday tasks are small, but they also play a part in protecting the environment. And if you alone do it, we will not be able to see the change in the environment for the better. But it takes the cooperation of many people to become a giant to protect the environment.
2 tháng 8 2015
a) \(A=\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+...+\frac{1}{120}\)
\(A=\frac{2}{20}+\frac{2}{30}+\frac{2}{42}+...+\frac{2}{240}\)
\(A=2\cdot\left(\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+...+\frac{1}{15\cdot16}\right)\)
\(A=2\cdot\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{15}-\frac{1}{16}\right)\)
\(A=2\cdot\left(\frac{1}{4}-\frac{1}{16}\right)=2\cdot\frac{3}{16}=\frac{3}{8}\)
b) \(B=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\)
\(B=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+...+\frac{5}{700}\)
\(B=\frac{5}{3}\cdot\left(\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}+...+\frac{3}{25\cdot28}\right)\)
\(B=\frac{5}{3}\cdot\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\right)\)
\(B=\frac{5}{3}\cdot\left(\frac{1}{4}-\frac{1}{28}\right)=\frac{5}{3}\cdot\frac{3}{14}=\frac{5}{14}\)
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