-25*72+25*21-49*25

=(-25).(72-21+49)

=(-25).100

=(-2500)

bn nhớ k nha

#\(HMeisukii\)

#\(yGLinh\)

21. didn’t go

22. isn’t painting

23. aren’t planting

24. Are they making

25. is repairing

26. is taking

27. is explaining

28. is studying

29. tries/ don’t think

30. passes

21. didn’t go

22. isn’t painting

23. aren’t planting

24. Are they making

25. is repairing

26. is taking

27. is explaining

28. is studying

29. tries/ don’t think

30. passes

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

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

C

c

C. 24 chữ cái.

16 explorer

17 dramatically

18 survival

19 challenging

20 unconscious

26D 27C 28A 29C 30B

41. Was called by the time I arrived.

42. About taking up a cookery course?

*) $n_{CO_2} = 0,1(mol) ; n_{H_2O} = 0,15(mol)$

Bảo toàn nguyên tố với O : $2n_{O_2} = 2n_{CO_2} + n_{H_2O}$

$\Rightarrow n_{O_2} = 0,175(mol)$
$\Rightarrow V_{O_2} = 0,175.22,4 = 3,92(lít)$

Đáp án C

**) Bảo toàn khối lượng : $m_A = m_{CO_2} + m_{H_2O} - m_{O_2}$
$= 0,1.44 + 2,7 - 0,175.32 = 1,5(gam)$

Đáp án A

bn ơi chụp ngang mk khó dọc quá bn chụp dọc ik

Câu 21:

\(\dfrac{V_{CO_2}}{V_{H_2O}}=\dfrac{4}{3}\Rightarrow\dfrac{n_{CO_2}}{n_{H_2O}}=\dfrac{4}{3}\)

Chọn n_CO2 = 4 (mol), n_H2O = 3 (mol)

⇒ n_Z = 4 - 3 = 1 (mol)

Gọi CTPT của Z là C_nH_2n-2

\(\Rightarrow n=\dfrac{n_{CO_2}}{n_Z}=4\)

Vậy: CTPT của Z là C₄H₆.

→ Đáp án: C

Câu 22:

Ta có: n_CO2 - n_H2O = 1,95 - 1,69 = 0,26 (mol) = n_ankin

⇒ n_anken = 0,78 - 0,26 = 0,52 (mol)

Có: n_Br2 = n_anken + 2n_ankin = 1,04 (mol)

\(\Rightarrow m_{Br_2}=1,04.160=166,4\left(g\right)\)

→ Đáp án: B