Ma Tuấn Dương
Giới thiệu về bản thân
Thử phiên bản mới
How are you doing? I hope you're doing well.
I'm writing to you today to share some tips on how I've been improving my English pronunciation. I know it can be a bit challenging sometimes, but with a bit of practice, it's definitely possible to make progress. First, I started by listening to native speakers on podcasts and YouTube videos. I paid close attention to how they pronounced certain words and phrases. I also used a dictionary with audio pronunciations to check words I was unsure about. Another thing that helped me a lot was recording myself speaking and then listening back to it. This allowed me to identify my mistakes and work on them. I also found it useful to practice tongue twisters and repeat sentences after the speakers. I hope these tips are helpful for you too! Let me know if you have any other tips. Best regards,Dương
1. She used to wear a special dress for family gatherings when she was a kid.
2. He usually takes notes in class because he needs to remember everything.
1. She used to wear a special dress for family gatherings when she was a kid.
2. He usually takes notes in class because he needs to remember everything.
3.I came across an old photo of my aunt while I was cleaning.
Nửa chu vi tam giác:
\(\frac{\left(\right. 10 + 17 + 21 \left.\right)}{2} = 24 \left(\right. c m \left.\right)\)
Diện tích tam giác:
\(S = \sqrt{24. \left(\right. 24 - 10 \left.\right) . \left(\right. 24 - 17 \left.\right) . \left(\right. 24 - 21 \left.\right)} = 84 \left(\right. c m^{2} \left.\right)\)
Nửa chu vi tam giác:
\(\frac{\left(\right. 10 + 17 + 21 \left.\right)}{2} = 24 \left(\right. c m \left.\right)\)
Diện tích tam giác:
\(S = \sqrt{24. \left(\right. 24 - 10 \left.\right) . \left(\right. 24 - 17 \left.\right) . \left(\right. 24 - 21 \left.\right)} = 84 \left(\right. c m^{2} \left.\right)\)
Nửa chu vi tam giác:
\(\frac{\left(\right. 10 + 17 + 21 \left.\right)}{2} = 24 \left(\right. c m \left.\right)\)
Diện tích tam giác:
\(S = \sqrt{24. \left(\right. 24 - 10 \left.\right) . \left(\right. 24 - 17 \left.\right) . \left(\right. 24 - 21 \left.\right)} = 84 \left(\right. c m^{2} \left.\right)\)
Nửa chu vi tam giác:
\(\frac{\left(\right. 10 + 17 + 21 \left.\right)}{2} = 24 \left(\right. c m \left.\right)\)
Diện tích tam giác:
\(S = \sqrt{24. \left(\right. 24 - 10 \left.\right) . \left(\right. 24 - 17 \left.\right) . \left(\right. 24 - 21 \left.\right)} = 84 \left(\right. c m^{2} \left.\right)\)
) \(2 x = 7 + x\)
\(\Leftrightarrow 2 x - x = 7\)
\(\Leftrightarrow x = 7\)
Vậy \(S = \left{\right. 7 \left.\right}\)
b) \(\frac{x - 3}{5} + \frac{1 + 2 x}{3} = 6\)
\(\Leftrightarrow \frac{3 \left(\right. x - 3 \left.\right)}{15} + \frac{5 \left(\right. 1 + 2 x \left.\right)}{15} = 6\)
\(\Leftrightarrow \frac{3 x - 9 + 5 + 10 x}{15} = 6\)
\(\Leftrightarrow 13 x - 4 = 90\)
\(\Leftrightarrow 13 x = 94\)
\(\Leftrightarrow x = \frac{94}{13}\)
Vậy \(S = \left{\right. \frac{94}{13} \left.\right}\).
Ta có \(V T = \frac{\frac{4 x^{2}}{y^{2}}}{\left(\left(\right. \frac{x^{2}}{y^{2}} + 1 \left.\right)\right)^{2}} + \frac{x^{2}}{y^{2}} + \frac{y^{2}}{x^{2}}\)
Đặt \(\frac{x^{2}}{y^{2}} = t \left(\right. t > 0 \left.\right)\) thì VT thành
\(\frac{4 t}{\left(\left(\right. t + 1 \left.\right)\right)^{2}} + t + \frac{1}{t}\)
\(= \frac{4 t}{\left(\left(\right. t + 1 \left.\right)\right)^{2}} + \frac{t^{2} + 1}{t}\)
\(= \frac{4 t}{\left(\left(\right. t + 1 \left.\right)\right)^{2}} + \frac{\left(\left(\right. t + 1 \left.\right)\right)^{2}}{t} - 2\)
Đặt \(\frac{\left(\left(\right. t + 1 \left.\right)\right)^{2}}{t} = u \left(\right. u \geq 4 \left.\right)\) (vì bất đẳng thức \(\left(\left(\right. a + b \left.\right)\right)^{2} \geq 4 a b\))
Khi đó \(V T = u + \frac{4}{u} - 2\)
\(= \frac{4}{u} + \frac{u}{4} + \frac{3 u}{4} - 2\)
\(\geq 2 \sqrt{\frac{4}{u} . \frac{u}{4}} + \frac{3.4}{4} - 2\)
\(= 2 + 3 - 2\)
\(= 3\)
\(\Rightarrow V T \geq 3\)
Dấu "=" xảy ra \(\Leftrightarrow u = 4\) \(\Leftrightarrow t = 1\) \(\Leftrightarrow x = \pm y\)
Vậy ta có điều phải chứng minh. Dấu "=" xảy ra \(\Leftrightarrow x = \pm y\)
Bài làm:
45 phút = 3/4 giờ
Gọi x là quãng đường AB
=> Thời gian đi của người đó là: x/15
=> Thời gian về của người đó là: x/12
Vì thời gian về nhiều hơn thời gian đi là 45 phút nên ta có phương trình như sau:
x/12 - x/15 =3/4
Giải phương trình: x/12 - x/15 = 3/4
=> (5x - 4x)/60 = 3/4
=> x/60 = 3/4
=> x = 60*3/4
=> x = 45 (thỏa mãn)
Vậy quãng đường AB dài 45 km