Chọn B

\(1,\\ a,=6x^4y^4-x^3y^3+\dfrac{1}{2}x^4y^2\\ b,=4x^3+5x^2-8x^2-10x+12x+15\\ =4x^3-3x^2+2x+15\\ 2,\\ a,=7\left(x^2-6x+9\right)=7\left(x-3\right)^2\\ b,=\left(x-y\right)^2-36=\left(x-y-6\right)\left(x-y+6\right)\\ 3,\\ \Leftrightarrow x\left(x^2-0,36\right)=0\\ \Leftrightarrow x\left(x-0,6\right)\left(x+0,6\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=0,6\\x=-0,6\end{matrix}\right.\)

Ok

won - were - were taking - would travel - were eating - didn't come - could finish - were not

1 is covered

2 was invited

3 were caused

4 is being built

5 wasn't stolen

6 would be stacked

7 was invented

8 were translated

9 will be canceled

10 has not been used

11 being caught

12 was invented

13 is believed

14 has been celebrated

15 painted

16 are being planted

17 was taken

18 to be recognized

1. He met many friends who encouraged him in his work.

2. He often tells me about the village where he was born.

3. Can you understand the question which he asked you last time?

4. The man whose son we play with every day is an architect.

5. The city where we spent our vacation was very beautiful.

6. The train which arrived two hours late broke down twice on the way.

7. I stopped in a smal ltown where my sister is working.

8. The book which I gave him was rather difficult.

9. The picture which you were talking about has been stolen.

10. She is the girl who I bought these roses for.

11. This morning I met Diana who I hadn't seen for ages.

12. Tulip computers which are made in Holland are very good.

13. I saw a girl whose beauty took my breath away.

14. John, whose mother is in hospital, is absent from school.