Ad ơi giúp em với ạ em cảm ơn 
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Mọi người ơi,giúp em bài với ạ em cảm ơn ạ
25 tháng 2 2022
ĐKXĐ: x>=0; x<>9
\(B=\dfrac{2x-6\sqrt{x}+x+3\sqrt{x}-3x-3}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\cdot\dfrac{\sqrt{x}-3}{\sqrt{x}+1}\)
\(=\dfrac{-3\sqrt{x}-3}{\sqrt{x}+3}\cdot\dfrac{1}{\sqrt{x}+1}=\dfrac{-3}{\sqrt{x}+3}\)
9 tháng 9 2021
\(\left(3x-4\right)^3=5^2+4.5^2\)
\(\Leftrightarrow\left(3x-4\right)^3=5^2\left(1+4\right)\)
\(\Leftrightarrow\left(3x-4\right)^3=5^3\)
\(\Leftrightarrow3x-4=5\Leftrightarrow3x=9\Leftrightarrow x=3\)
9 tháng 9 2021
Ta có: \(\left(3x-4\right)^3=5^2+4\cdot5^2\)
\(\Leftrightarrow3x-4=5\)
hay x=3
AH
Akai Haruma
Giáo viên
4 tháng 9 2021
Lời giải:
$A=7+(7^2+7^3+7^4+7^5)+(7^6+7^6+7^8+7^9)+....+(7^{2018}+7^{2019}+7^{2020}+7^{2021})$
$=7+7^2(1+7+7^2+7^3)+7^6(1+7+7^2+7^3)+....+7^{2018}(1+7+7^2+7^3)$
$=7+(1+7+7^2+7^3)(7^2+7^6+....+7^{2018}$
$=7+400(7^2+7^6+....+7^{2018})$
Dễ thấy $400(7^2+7^6+....+7^{2018})$ tận cùng là $0$
Do đó $A$ tận cùng là $7$
12 tháng 9 2021
\(3\left(x+2\right)^3-1^{2019}=5\cdot4^2\)
\(\Leftrightarrow3\left(x+2\right)^3=5\cdot16+1=81\)
\(\Leftrightarrow x+2=3\)
hay x=1
MH
12 tháng 9 2021
\(4^{15}.9^{15}< 2^n.3^n< 18^{16}.2^{16}\)
⇒\(\left(4.9\right)^{15}< \left(2.3\right)^n< \left(18.2\right)^{16}\)
⇒\(\left(6^2\right)^{15}< 6^n< \left(6^2\right)^{16}\)
⇒\(6^{30}< 6^n< 6^{32}\)
⇒\(6^n=6^{31}\)
⇒n=31
12 tháng 9 2021
\(4^{15}\cdot9^{15}< 2^n\cdot3^n< 18^{16}\cdot2^{16}\\ \Leftrightarrow\left(4\cdot9\right)^{15}< \left(2\cdot3\right)^n< \left(18\cdot2\right)^{16}\\ \Leftrightarrow36^{15}< 6^n< 36^{16}\\ \Leftrightarrow6^{30}< 6^n< 6^{32}\\ \Leftrightarrow n=31\)
Question 9:
Currently, there are many types of pollution around us, noise pollution is one of them. Noise pollution is noise in the environment that exceeds a certain threshold that is annoying to humans or animals. Outdoor noise can also be summed up from environmental noise. It may be due to volcanic activity and earthquakes, but this is only a minor cause, the main reason is us. Currently, vehicles are increasing with dizziness, causing noise pollution due to engine noise, sirens as well as vehicle brakes. It is quite common, and it also causes a lot of harm to humans and other animals. Noise pollution adversely affects psychological and mental health, can cause high blood pressure, stress, tinnitus, hearing loss, sleep disturbances, and other harm. timely remedy: Limiting traffic on the street, sharing, using public transport; Using jet engines without noise for planes; Planting many trees on both sides of the road; restrict the use of machinery and equipment that emit a lot of noise, replace old, expired equipment; Use physical barriers at work; Use thermal equipment. Noise pollution is a very serious problem, I hope it will be fixed in the future
Question 8:
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.