Giúp mình hai câu này vs mình k bt làm 
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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 ......
\(b,\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18+\dfrac{1}{y}\\5.\left(18+\dfrac{1}{y}\right)+\dfrac{4}{y}=51\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18+\dfrac{1}{y}\\\dfrac{9}{y}=-39\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18-\dfrac{13}{3}\\\dfrac{1}{y}=\dfrac{-13}{3}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=\dfrac{41}{3}\\\dfrac{1}{y}=\dfrac{-13}{3}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{3}{41}\\y=\dfrac{-3}{13}\end{matrix}\right.\)
8 tháng 4 2023
- Bài này phải có điều kiện \(x>0\) thì mới làm được nhé bạn.
NH
9 tháng 4 2023
À mình cảm ơn bạn nhá mình cũng vừa mới xem lại đề cô gửi thì mình thấy có điều kiện x>0 thật mình cảm ơn bạn nhiều nhá
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.
AM
20 tháng 2 2022
Câu 13:
Ta có: \(f\left(x\right)>0\Leftrightarrow3x-m>0\Leftrightarrow3x>m\)
Mà x>1 hay 3x>3
Vậy \(m\le3\)
Đáp án C
AM
20 tháng 2 2022
Câu 14:
(d): x-2y+1=0 hay \(\dfrac{1}{2}x+\dfrac{1}{2}=y\)
Gọi phương trình đường thẳng cần tìm là: y=ax+b
Phương trình cần tìm đi qua A nên ta có: 2=-2a+b
Để phương trình cần tìm vuông góc với (d) thì: \(a.\dfrac{1}{2}=-1\Rightarrow a=-2\)\(\Rightarrow b=-2\)
Vậy phương trình cần tìm là: \(y=-2x-2\)
Đáp án C
LP
13 tháng 2 2022
Travelling by train is slower but more interesting than travelling by plane.
My brother worked as an engineer for a printing factory last year.
We had to cancel the picnic because of that heavy storm
I believe that you will be impressed by the beauty of the city
cái này là đề thi hay là gì vậy ?
Nếu là đề thi thì ko giúp đc đâu :>