Câu hỏi của xhok du ki - Toán lớp 6 - Học toán với OnlineMath

Khi ta rót nước gần đầy bình, cột không khí trong phích sẽ dao động mạnh và phát ra âm to nên những người có kinh nghiệm có thể ước lượng đc

Xét : \(\left\{\begin{matrix}\left(x-8\right)^{2016}\ge0\\\sqrt{y-10}\ge0\end{matrix}\right.\)

=> Để \(\left(x-8\right)^{2016}+\sqrt{y-10}=0\)

Thì ( x- 8)²⁰¹⁶= \(\sqrt{y-10}\)= 0

\(\Rightarrow\left\{\begin{matrix}\left(x-8\right)^{2016}=0\\\sqrt{y-10}=0\end{matrix}\right.\Rightarrow\left\{\begin{matrix}x=8\\y=10\end{matrix}\right.\)

=> x+ y= 8+ 10= 18

Vậy x+ y= 18

Gọi thời gian đi với vận tốc 40km/ h là t₁

Gọi thời gian đi với vận tốc 50km/ h là t₂

=> t₁. 40= t₂. 50

=> \(\frac{t_1}{50}=\frac{t_2}{40}=\frac{t_1-t_2}{50-40}\)

=> \(\frac{0,3}{10}=0,03\left(h\right)\)

=> t₁= 0,03. 50= 1,5 (h)

=> t₂= 0,03. 40= 1,2 (h)

=> Thời gian dự định là: 1,5+ 1,2+ 0,3= 3 (h)

Khi âm truyền đến tai thì bề mặt tai gồ ghề sẽ hấp thụ âm tốt hơn cho ta nghe rõ hơn

Last summer, I and my friends go to Vung Tau by motobike. we have two interesting days in Vung Tau city. We start my trip on 6h AM. after 1 hour, We get to Long Thanh stop stations. we have stopped there for 15 minutes anh drink fresh cow's milk. Then we continue my trip to vung tau city. after 1 hour we get vung tau city. many hotel and motel but we had to spend hard 1 hour to look up a hotel for staying. the hotel which we stay is a small nice hotel, from our hotel we can see the beach and it had a good view. Because we have a long trip by motobike so that we are very tired. after check in we only want to sleeping. I don't know, what do other peoples do but when I wake up and walk to outside. I see my friends drinking coffee. at that 2 o'clock PM. we have spent 2 hours for drinking coffee after that we go to the beach to swim. at the evening, we have a round in vung tau by motobike. verybody want to see vung tau by night until 10 o'clock we return back our hotel. and all night, we play card togethe. on the morning tomorrow. we walk to the beach and swim with the local peoples and anothe tourists. after that we go to coffee shop and chat togethe. until 12 o'clock we have lunch and 3 o'clock we come back to hcm city. we arrived hcm at 5 o'clock. we bye togethe. and end 2 interesting day in vung tau.

cách 1:

áp dung bất đẳng thức Cô-si ta có:

\(\frac{a}{2}+\frac{b}{2}\ge2\sqrt{\frac{a}{2}.\frac{b}{2}}=\sqrt{a.b}\)(1)

\(\frac{b}{2}+\frac{c}{2}\ge2\sqrt{\frac{b}{2}.\frac{c}{2}}=\sqrt{b.c}\)(2)

\(\frac{c}{2}+\frac{a}{2}\ge2\sqrt{\frac{c}{2}.\frac{a}{2}}=\sqrt{c.a}\)(3)

cộng 2 vế (1);(2) và (3) ta được:

\(\frac{a}{2}+\frac{b}{2}+\frac{b}{2}+\frac{c}{2}+\frac{c}{2}+\frac{a}{2}\ge\sqrt{a.b}+\sqrt{b.c}+\sqrt{c.a}\)

\(\Leftrightarrow a+b+c\ge\sqrt{a.b}+\sqrt{b.c}+\sqrt{c.a}\)(điều phải chứng minh)