Bài 2: Chọn C

Bài 4: 

a: \(\widehat{C}=180^0-80^0-50^0=50^0\)

Xét ΔABC có \(\widehat{A}=\widehat{C}< \widehat{B}\)

nên BC=AB<AC

b: Xét ΔABC có AB<BC<AC

nên \(\widehat{C}< \widehat{A}< \widehat{B}\)

1: ĐKXĐ: n>=2

Ta có: \(3\cdot C_{n+1}^3-3\cdot A_{n}^2=52\left(n-1\right)\)

=>\(3\cdot\frac{\left(n+1\right)!}{\left(n+1-3\right)!\cdot3!}-3\cdot\frac{n!}{\left(n-2\right)!}=52\left(n-1\right)\)

=>\(\frac{3\cdot\left(n+1\right)\cdot n\cdot\left(n-1\right)}{6}-3n\left(n-1\right)=52\left(n-1\right)\)

=>\(\frac{n\left(n+1\right)\left(n-1\right)}{2}-\frac{6n\left(n-1\right)}{2}=52\left(n-1\right)\)

=>n(n+1)(n-1)-6n(n-1)=104(n-1)

=>(n-1)(n^2+n-6n)=104(n-1)

=>(n-1)(n^2-5n-104)=0

=>\(n^2-5n-104=0\)

=>(n-13)(n+8)=0

=>n=13(nhận) hoặc n=-8(loại)

a: ảnh của M(4;5) qua phép tịnh tiến theo \(\overrightarrow{v}=\left(3;-1\right)\) là:

\(\begin{cases}x=4+3=7\\ y=5+\left(-1\right)=4\end{cases}\)

b: Gọi (d'): ax+by+c=0 là ảnh của (d) qua phép tịnh tiến theo \(\overrightarrow{v}=\left(3;-1\right)\)

=>(d'): 2x-3y+c=0

Lấy A(1;3) thuộc (d)

Gọi A'(x;y) là ảnh của A qua phép tịnh tiến theo \(\overrightarrow{v}=\left(3;-1\right)\)

=>A' thuộc (d')

Tọa độ A' là:

\(\begin{cases}x=1+3=4\\ y=3-1=2\end{cases}\)
Thay x=4 và y=2 vào (d'), ta được:

\(2\cdot4-3\cdot2+c=0\)

=>8-6+c=0

=>c+2=0

=>c=-2

Vậy: (d'): 2x-3y-2=0

1 Last week the doctor advised him not to swim in a few weeks

2 William Shakespeare was born on April 23th, 1564

3 He was the eldest son of a wealthy glove maker

4 He got married to Anne Hathaway and had three children

5He moved to Lon don in 1588 and joined in a theatrical company

1. last week, the doctor advised me not to swim few weeks

2. william shakespeare was born on april 23th 1564

3. he is the eldest son of wealthy golve maker

4. he married anne hathaway and had three children

Bài 5: 

A[-2;10)

\(A\cup B=\left(-\infty;10\right)\)

\(A\cap B=\varnothing\)

A\B=[-2;10)

B\A=(-\(\infty\);-3)