1 bài 1 tích . uy tín cực kì,bài hay cho 2 tích

My name is ........., and I am the only son in my family. I am ..... years oldt, and I am currently studying in ......... My little family has four people, and we live in ............ province. The house is always filled with my dad’s laughter, my mother’s warm voice and my sister’s playfulness.

My father is a retired police officer, and he is working as a defense education teacher in our local high school. Perhaps he had to due with years of hard training in the military; my father is finally comfortable to show his humor in the teaching environment. In the first look, he is a tough man; but actually he is very emotional and funny. Dad is a solid pillar and a great spiritual supporter for the whole family.

Un him, my mother is a gentle but strict woman. many other women, my mother always takes care and sacrifices the best things for us. She is both our close friends and tutor in study and some private problems.

My sister is going to be a high school student soon. She is doing very well at school, and she is always rewarded by the school. She starts to look a mature girl, un the little monkey that always sks to me the previous years.

This summer I cannot go home to visit my family and play with my sister because I am about to graduate. I miss them a lot, and I hope that all will be over soon so I can return home and work near my beloved family.

Những chỗ ..... bạn tự điền 

cảm ơn bạn nhìu ,mk đã tích cho bn rồi đó

hơi dài bn ạ

Nhỏ quá

Đề bài là: Tính cos2x 

Cảm ơn mn nhiều ạ!

`sin3x sinx+sin(x-π/3) cos (x-π/6)=0`

`<=> 1/2 (cos2x - cos4x) + 1/2(-sin π/6 + sin (2x-π/2)=0`

`<=> cos2x-cos4x-1/2+ sin(2x-π/2)=0`

`<=>cos2x-cos4x-1/2+ sin2x .cos π/2 - cos2x. sinπ/2=0`

`<=> cos2x - cos4x - cos2x = 1/2`

`<=> cos4x = cos(2π)/3`

`<=>` \(\left[{}\begin{matrix}4x=\dfrac{2\text{π}}{3}+k2\text{π}\\4x=\dfrac{-2\text{π}}{3}+k2\text{π}\end{matrix}\right.\)

`<=>` \(\left[{}\begin{matrix}x=\dfrac{\text{π}}{6}+k\dfrac{\text{π}}{2}\\x=-\dfrac{\text{π}}{6}+k\dfrac{\text{π}}{2}\end{matrix}\right.\)

\(sin3x.sinx+sin\left(x-\dfrac{\pi}{3}\right)cos\left(x-\dfrac{\pi}{6}\right)=0\)

\(\Leftrightarrow\dfrac{1}{2}cos2x-\dfrac{1}{2}cos4x+\dfrac{1}{2}sin\left(2x-\dfrac{\pi}{2}\right)+\dfrac{1}{2}sin\left(-\dfrac{\pi}{6}\right)=0\)

\(\Leftrightarrow\dfrac{1}{2}cos2x-\dfrac{1}{2}cos4x-\dfrac{1}{2}cos2x-\dfrac{1}{4}=0\)

\(\Leftrightarrow cos4x+\dfrac{1}{2}=0\)

\(\Leftrightarrow2cos^22x-1+\dfrac{1}{2}=0\)

\(\Leftrightarrow cos^22x=\dfrac{1}{4}\)

\(\Rightarrow cos2x=\pm\dfrac{1}{2}\)

Bài 9.

Diện tích lưỡi dao: \(S=20\cdot10^{-2}\cdot0,05\cdot10^{-3}=10^{-5}\left(m^2\right)\)

Áp suất tác dụng lên lưỡi dao: 

\(p=\dfrac{F}{S}=\dfrac{40}{10^{-5}}=4\cdot10^6Pa\)

Bài 10.

a)Diện tích tiếp xúc: \(S=2\cdot10\cdot10^{-4}=2\cdot10^{-3}m^2\)

Áp suất tác dụng lên mặt sàn: 

\(p=\dfrac{F}{S}=\dfrac{P}{S}=\dfrac{500}{2\cdot10^{-3}}=25\cdot10^4Pa\)

bDiện tích tiếp xúc của chân bạn Lan: \(S=2\cdot150=300cm^2=0,03m^2\)

Áp suất tác dụng lên mặt sàn:

\(p=\dfrac{F}{S}=\dfrac{500}{0,03}=\dfrac{50000}{3}Pa\)

Bài 15.

Trọng lượng của bạn Minh và ghế: \(P=10m=10\cdot\left(36+4\right)=400N\)

Áp suất của các chân ghế lên mặt sàn: 

\(p=\dfrac{P}{S}=\dfrac{400}{19,3\cdot10^{-4}}=207253,886Pa\)

Bài 16.

a)Áp suất tác dụng lên pittong nhỏ:

\(p=\dfrac{f}{s}=\dfrac{600}{15\cdot10^{-4}}=4\cdot10^5Pa\)

b)Lực tác dụng lên pittong lớn:

\(\dfrac{F}{f}=\dfrac{S}{s}\Rightarrow\dfrac{F}{600}=\dfrac{150}{15}\Rightarrow F=6000N\)

Bài 17.

Diện tích tiếp xúc: \(S=0,015\cdot2=0,03m^2\)

Trọng lượng của người đó: \(P=F=p\cdot S=2\cdot10^4\cdot0,03=600N\)

Khối lượng người đó: \(m=\dfrac{P}{10}=\dfrac{600}{10}=60kg\)

Bài 1 : bằng phân số ban đầu

Bài 2 : nhỏ hơn phân số ban đầu

Bài 3 : lớn hơn phân số ban đầu