Bài 3:

theo đề bài ta có:

\(\left\{{}\begin{matrix}2a-3b=0\\5b-7c=0\\3a-7b+5c=30\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=42\\b=28\\c=20\end{matrix}\right.\)

Bài 4: 

Đặt \(\dfrac{x}{4}=\dfrac{y}{5}=\dfrac{z}{6}=k\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=4k\\y=5k\\z=6k\end{matrix}\right.\)

Ta có: \(x^2-2y^2+z^2=18\)

\(\Leftrightarrow16k^2-50k^2+36k^2=18\)

\(\Leftrightarrow k^2=9\)

Trường hợp 1: k=3

\(\Leftrightarrow\left\{{}\begin{matrix}x=4k=4\cdot3=12\\y=5k=5\cdot3=15\\z=6k=6\cdot3=18\end{matrix}\right.\)

Trường hợp 2: k=-3

\(\Leftrightarrow\left\{{}\begin{matrix}x=4k=-3\cdot4=-12\\y=5k=-3\cdot5=-15\\z=6k=-3\cdot6=-18\end{matrix}\right.\)

I remembered the time when I was at home with my mom. I used to wish I could run away to a new place to live on my own. And that day came. I had to go to a big city for study and that was the first time I've known that I love my family that much. I used to cry every night before going to bed.
One day I read a poem about Mom and Child. It told a story about a mother who gave her all to her children, worried about them all her life and never hoped for requital. One day the mother went away forever and her child realized that now she is a mother, she understood her mother more and she missed her mother more than ever.
I cried each time I read that poem. I dont know what came into me and what made me cry that much. It was a very normal poem, just like the other ones I read when I was in school. And the first time I got a phone call from her, I couldnt help myself from bursting into tears. I love her, my mother!
Now I'm living abroad and have to do everything on my own. The thing I concern most about is my family members' health. Some bad dreams can make me worry all day. I wish good health for my family and especially, my mom!

Mother , she is the best in my life. I can not say how much love her . I please her so much since she gave me bỉth brings me love and grows me up. She teaches me what is a good person. She always yells me(and that is the only thing I don't love very much from her ). But you know, she just takes care of me a lot. Every day , she tells me e same words :" Have you taken your medicine ? Have you drunk milk? You know what time it is now?..........." Yah ! If you were me , you may feel very tired. But I have learned in a story that :" You are a happy child having mother and sad for who don't have."
You may be tired listenning to her words everyday, but please image one day you don't see her any longer, can't listen her voice. What would you feel. Yes, you would say : I've never loved her than this moment.

Còn 7,25 kg nhé bạn!!!

Học tốt!!!

Giải:

Sau khi lấy ra 10,5 kg gạo thì trong thùng còn:

     26,75 - 10,5 = 16,25 ( kg )

Trong thùng còn số ki - lô - gam gạo là:

     16,25 - 9 = 7,25 ( kg )

                    Đáp số: 7,25 kg gạo.

~ Thực sự thì cũng không phiền đâu em ạ :)) ~

số gạo còn lại sau khi lấy 10,5 kg là

\(26,75-10,5=16.25\left(kg\right)\)

Sos gạo còn lại cuối cùng là

\(16,25-9=7,25\left(kg\right)\)

Đ/S:......

Học tốt và đừng bơ anh nhé 

mik đang cần gấp!

ai trả lời nhanh, đúng yêu cầu k đúng luôn

ai trả lời nhanh. đúng yêu cầu k đúng luôn!

mik cx như bn

ok

mình cũng học ở phần mềm này nè, vui lắm

uk hihihi ban ten j

Mình tên Đỗ Ánh Nguyệt, còn bạn tên j

...

ý là ảnh chụp màn hình ạ

ko phải lớp 4:(((