21 which

defining

22 which

defining

23 which

defining

24 who

non-defining

25 that

defining

26 whose

defining

27 who

non-defining

28 that

defining

29 which

non-defining

30 whose

defining

30B 31B 32D 33D 34C 35B 36B 37C 38B 39A 40D 41D 42A 43D 44D 45A 46C 47B 48C 49B 50C 51C 52B 53D 54B 55C 56A 57C 58A 59D 60B

30B 31B 32D 33D 34C 35B 36B 37C 38B 39A 40D 41D 42A 43D 44D 45A 46C 47B 48C 49B 50C 51C 52A 53D 54B 55C 56A 57C 58A 59D 60B

1 It was silly to lend him money

2 Meeting the president is exciting

3 While we were on the summer holiday, we were so happy

4 While they were playing, they cried twice

5 Writing good composition in English was not easy

26 It was silly to lend him money
27 Meeting the president is exciting
28 While we were in the summer holiday, we were happy
29 While the play was being played, they cried twice
30 Writing good compositions in English was not easy

Đề ở đâu vậy bạn?

\(\left\{{}\begin{matrix}x_1+x_2=2\\x_1x_2=-1\end{matrix}\right.\)

8: \(=\dfrac{x_1^2+x_2^2}{\left(x_1\cdot x_2\right)^2}=\dfrac{2}{1}=2\)

9: \(=\left(x_1+x_2\right)^3-3x_1x_2\left(x_1+x_2\right)=2^3-3\cdot\left(-1\right)\cdot2=8+6=14\)

16: \(=\sqrt{\left(x_1+x_2\right)^2-4x_1x_2}=\sqrt{2^2-4\cdot\left(-1\right)}=\sqrt{4+4}=2\sqrt{2}\)

 1-2+3-4+5-6+...+19-20+21

= 1 + ( 3 - 2 ) + ( 5 - 4 ) + ( 7 - 6 ) + ... + ( 19 - 18 ) + ( 21 - 20 )

= 1 + 1 + 1 + ... + 1 + 1   ( có 11 số 1 )

= 11