ai bt làm bài này k?
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16 tháng 2 2022
a, \(\left\{{}\begin{matrix}35x-28y=21\\35x-45y=40\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}17y=-19\\x=\dfrac{3+4y}{5}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{19}{17}\\x=-\dfrac{13}{17}\end{matrix}\right.\)
b, Đặt x;y khác 0
Đặt 1/x = t ; 1/y = u
\(\left\{{}\begin{matrix}t-8u=18\\5t+4u=51\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}5t-40u=90\\5t+4u=51\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-44u=39\\t=18+8u\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}u=-\dfrac{39}{44}\\t=\dfrac{120}{11}\end{matrix}\right.\)
Theo cách đặt y = -44/39 ; x = 11/120 (tm)
16 tháng 2 2022
\(a,\\ \Leftrightarrow\left\{{}\begin{matrix}35x-28y=21_{\left(1\right)}\\35x-45y=40_{\left(2\right)}\end{matrix}\right.\\ Lấy\left(1\right)-\left(2\right),ta.đc:\\ -17y=19\Leftrightarrow y=\dfrac{-19}{17}\\ Thay.vào.\left(1\right):\\ 35x-28.\dfrac{-19}{17}=21\Leftrightarrow x=\dfrac{-5}{17}\)
Vậy ......
\(b,\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18+\dfrac{1}{y}\\5.\left(18+\dfrac{1}{y}\right)+\dfrac{4}{y}=51\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18+\dfrac{1}{y}\\\dfrac{9}{y}=-39\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18-\dfrac{13}{3}\\\dfrac{1}{y}=\dfrac{-13}{3}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=\dfrac{41}{3}\\\dfrac{1}{y}=\dfrac{-13}{3}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{3}{41}\\y=\dfrac{-3}{13}\end{matrix}\right.\)
2 tháng 9 2021
sin 650=cos 350
\(cos70^0=sin30^0\)
\(tan80^0=cot20^0\)
\(cot68^0=tan32^0\)
7 tháng 8 2021
1.
a) Mary is as thin as her brother.
b) A lemon is not as sweet as an orange.
c) A donkey cannot run as quick as a horse.
d) This dress is twice as pretty as that one.
e)They don't drive a car as dangerous as us.
7 tháng 8 2021
1. So sánh ngang bằng.
a. Mary/thin/her brother.
Mary is as thin as her brother.
b. A lemon/not sweet/ an orange.
A lemon isn't as sweet as an orange.
c. A donkey/not run/quick/ a horse.
A donkey doesn't run as quickly as a horse.
d. This dress/twice/pretty/that one.
This dress is twice as pretty as that one.
e. They/ drive a car/ dangerous/ we.
They drive a car as dangerously as we do.
2. So sánh hơn: (Nhấn mạnh các câu ss hơn)
a. this film /popular/ that one.
This film is much more popular than that one.
b. A bird/can fly/slow/ a plane.
A bird can fly much more slowly than a plane.
c. Ba/ friendly/ Nam.
Ba is much more friendly than Nam.
d .Your house/far/from school /my house.
Your house is much farther from school than my house.
e. My father / drive/ careful/ I
My father drives much more carefully than I do.
3. So sánh nhất: (Nhấn mạnh theo 2 cách đã học)
a. This road/short /way/ in the city.
This road is by far the shortest way in the city.
b. Lan/ walk/ slow / in my class.
Lan walks by far the most slowly in my class.
c. Indian tea/bad/ of all.
Indian tea is by far the worst of all.
d. Anna/ work/ simple/girl/ in the world.
Anna works by far the simplest girl in the world.
e. Jack/ can tell/ the stories/ humourous/ in the world.
Jack can tell the stories by far the most humorously in the world.
II. Rewrite these sentences
1. This street is narrower than that one
Þ That street isn't as wide as this one.
Þ That street is wider than this one.
2. Linda drives more carefully than Peter
Þ Peter doesn't drive as carefully as Linda.
Þ Peter drives more carelessly than Linda.
3.Your car is more convenient than mine
Þ My car isn't as convenient as yours.
Þ My car is less convenient than yours.
4. We behave more politely than her
Þ She doesn't behave as politely as us.
Þ She behaves more impolitely than us.
5.I cook better than my mother
Þ my mother doesn't cook as well as me.
Þ my mother cooks worse than me.
6. Anna isn’t as confident as me
=> I am more confident than Anna.
7. This book isn’t as boring as that one
Þ That book is more boring than this one.
8. I don’t work as effectively as he does
=> He works more effectively than I do.
9. My bedroom isn’t so comfortable as yours
Þ Your bedroom is more comfortable than mine.
10. John didn’t speak English as well as Mary
=> Mary spoke English better than John.
11. Peter can dance the most gracefully in my city
=> No one in my city can dance as gracefully as Peter.
=> No one in my city can dance more gracefully than Peter.
12. Kangaroo is the most unique animal in the world
=> No animal in the world is as unique as kangaroo.
=> No animal in the world is more unique than kangaroo.
13. No river in the world is longer than Nile
=> Nile is the longest river in the world.
14. No student in my class learns Maths more intelligently than John
=> John learns Maths the most intelligently in my class.
15. If you read many books, you will have much knowledge
→ The more books you read, the more knowledge you will have.
16. He speaks too much and people feel bored.
→ The more he speaks, the more bored people feel.
8 tháng 10 2023
trả lời
5x-3 -20 = 105
5x-3 = 105 + 20
5x-3 = 125
5x-3 = 53
x-3 = 3
x =3+3
x = 6
Vậy x = 6
PM
2
TP
Thảo Phương
CTVVIP
30 tháng 8 2021
\(n_{HCl}=\dfrac{1}{36,5}=0,027\left(mol\right)\)
\(n_{NaOH}=\dfrac{1}{40}=0,025\left(mol\right)\)
\(HCl+NaOH\rightarrow NaCl+H_2O\)
Lập tỉ lệ : \(\dfrac{0,027}{1}>\dfrac{0,025}{1}\)=> Sau phản ứng HCl dư
Vậy khi nhúng quỳ tím vào dung dịch sau phản ứng, quỳ tím hóa đỏ
PM
1
DT
Đỗ Thanh Hải
CTVVIP
5 tháng 9 2021
1 hadn't seen - were
2 doesn't like - being phoned
3 is eaten
4 is leaving - will wait
5 won't be - will you go
6 is coming - don't want
7 hasn't read - have gone
8 haven't seen - left
9 was washing - was writing
10 sets - goes
11 were talking - walked
12 has stayed - studied - was
13 was made
14 had told - went away
15 will be held
16 had gone - sat - rested
17 watched - had done
PM
1
DT
Đỗ Thanh Hải
CTVVIP
5 tháng 9 2021
1 is grown in many countries in the world
2 was invented by Graham bell many years ago
3 has been used for many years
4 Is English practiced by Lan everyday
5 will be taken out of the city
6 can this letter be sent by Mary 2 days ago
7 is being made from vegetables
8 must be finished before Sunday
9 hadn't been used for a long time
10 Will I be met at the airport by Jack tomorrow
12 It is thought that Maradona is.....
13 It has been believed that the job is.....
14 It was explained that this powerful.....
NT
0
Số học sinh ở hai lớp 4B và 4C là: 90-30=60(bạn)
Số học sinh ở lớp 4B là (60+2):2=31(bạn)
Số học sinh ở lớp 4C là 31-2=29(bạn)