1.there used to be a clinic here in 1800s

2.we often used to go to the movie 

3.Luke didn't use to wear uniform to school,so.....

4.we used to play the game of dragon -snake when we were children 

5.my sister usually used to write in her diary before going to bed

6.my father used to use public transport to go to work when he lived in Japan

7.Daisy used to be able to speak Chinese

8.I used to have long hair a few years ago

9.my grandfather didn't use to drink a cup of coffee every morning.....when he was....

10.Helen used to lose when she played chess with her elder brother

'Police' (n): cảnh sát luôn luôn là số nhiều và dùng với động từ ở số nhiều. VD: cattle (gia súc),... Bạn hiểu chưa?

police luôn luôn là số nhiều 

policeman mới là số ít

4. \(x^2-3x+xy-3y=0\)

\(\Leftrightarrow x\left(x-3\right)+y\left(x-3\right)=0\)

\(\Leftrightarrow\left(x-3\right)\left(x+y\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\x+y=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-y\end{matrix}\right.\)

5. \(x^2-8x-3x+24=0\)

\(\Leftrightarrow x\left(x-8\right)-3\left(x-8\right)=0\)

\(\Leftrightarrow\left(x-8\right)\left(x-3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-8=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=8\\x=3\end{matrix}\right.\)

6. \(\left(x-2\right)^2-5\left(2-x\right)=0\)

\(\Leftrightarrow\left(x-2\right)^2+5\left(x-2\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left(x-2+5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x-2+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)

7. \(3x\left(x-1\right)-x^2+2x-1=0\)

\(\Leftrightarrow3x\left(x-1\right)-\left(x^2-2x+1\right)=0\)

\(\Leftrightarrow3x\left(x-1\right)-\left(x-1\right)^2=0\)

\(\Leftrightarrow\left(x-1\right)\left[3x-\left(x-1\right)\right]=0\)

\(\Leftrightarrow\left(x-1\right)\left(2x+1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\2x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-\dfrac{1}{2}\end{matrix}\right.\)

8. \(x^2\left(x-3\right)+18-6x=0\)

\(\Leftrightarrow x^2\left(x-3\right)-6\left(x-3\right)=0\)

\(\Leftrightarrow\left(x-3\right)\left(x^2-6\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\x^2-6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=\pm\sqrt{6}\end{matrix}\right.\)

10. \(\left(x-5\right)^2-\left(x-2\right)^2=0\)

\(\Leftrightarrow\left[\left(x-5\right)-\left(x-2\right)\right]\left[\left(x-5\right)+\left(x-2\right)\right]=0\)

\(\Leftrightarrow\left(x-5-x+2\right)\left(x-5+x-2\right)=0\)

\(\Leftrightarrow-3\left(2x-7\right)=0\)

\(\Leftrightarrow2x-7=0\)

\(\Leftrightarrow x=\dfrac{7}{2}\)

12. \(x^2\left(x-3\right)-4x+12=0\)

\(\Leftrightarrow x^2\left(x-3\right)-4\left(x-3\right)=0\)

\(\Leftrightarrow\left(x^2-4\right)\left(x-3\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left(x+2\right)\left(x-3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x+2=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-2\\x=3\end{matrix}\right.\)

14. \(3x^2-7x-10=0\)

\(\Leftrightarrow3x^2+3x-10x-10=0\)

\(\Leftrightarrow3x\left(x+1\right)-10\left(x+1\right)=0\)

\(\Leftrightarrow\left(x+1\right)\left(3x-10\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\\3x-10=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=\dfrac{10}{3}\end{matrix}\right.\)

#Urushi

4: x^2-3x+xy-3y=0

=>x(x-3)+y(x-3)=0

=>(x-3)(x+y)=0

=>x=3 và x+y=0

=>x=3 và y=-3

6: (x-2)^2-5(2-x)=0

=>(x-2)^2+5(x-2)=0

=>(x-2)(x-2+5)=0

=>(x-2)(x+3)=0

=>x=-3 hoặc x=2

8: x^2(x-3)+18-6x=0

=>x^2(x-3)-6(x-3)=0

=>(x-3)(x^2-6)=0

=>x=3 hoặc \(x=\pm\sqrt{6}\)

10: (x-5)^2-(x-2)^2=0

=>(x-5-x+2)(x-5+x-2)=0

=>-3(2x-7)=0

=>2x-7=0

=>x=7/2

12: x^2(x-3)-4x+12=0

=>x^2(x-3)-4(x-3)=0

=>(x-3)(x^2-4)=0

=>(x-3)(x-2)(x+2)=0

=>\(x\in\left\{3;2;-2\right\}\)

14: 3x^2-7x-10=0

=>3x^2-10x+3x-10=0

=>(3x-10)(x+1)=0

=>x=10/3 hoặc x=-1

Xét tứ giác ABCD có:

A + B + C + D = 360 độ(theo định lý)

Suy ra C = 360 độ - ( A + B + D)

                360 độ - 240 độ

                 120 độ

Vậy...

Bạn thêm ký hiệu góc vào giúp mình.