\(a)3784+23-3785-15\)

\(= \left(3784-3785\right)+\left(23-15\right)\)

\(=-1+8=7\)

\(b)21+22+23+24-11-12-13-14\)

\(=\left(21-11\right)+\left(22-12\right)+\left(23-13\right)+\left(24-14\right)\)

\(=10+10+10+10=40\)

a)3784+23-3785-15=(3784-3785)+(23-15)=(-1)+8=7

b)21+22+23+24-11-12-13-14=(21-11)+(22-12)+(23-13)+(24-14)

=10+10+10+10=4X10=40

Học tốt

Câu 21:

\(C_nH_{2n-2}+AgNO_3+NH_3\rightarrow C_nH_{2n-3}Ag+NH_4NO_3\\ n_X=\dfrac{14-5,44}{108-1}=0,08\left(mol\right)=n_{kết.tủa}\\ M_{C_nH_{2n-3}Ag}=\dfrac{14}{0,08}=175\left(\dfrac{g}{mol}\right)=14n+107\\ \Leftrightarrow n=5\\ \Rightarrow CTPT.X:C_5H_8\\ CTCT:CH\equiv C-CH_2-CH_2-CH_3\\ CH_3-C\equiv C-CH_2-CH_3\\ CH\equiv C-CH\left(CH_3\right)-CH_3\)

Chọn C

Câu 22: 

\(n_{C_2H_2}=\dfrac{2,24}{22,4}=0,1\left(mol\right)\\ C_2H_2+2Br_2\rightarrow C_2H_2Br_4\\ n_{Br_2}=2.n_{C_2H_2}=2.0,1=0,2\left(mol\right)\\ m_{Br_2}=0,2.160=32\left(g\right)\\ Chọn.A\)

Câu 23:

\( PTHH:C_2H_2+2Br_2\rightarrow C_2H_2Br_4\left(1\right)\\ C_2H_4+Br_2\rightarrow C_2H_4Br_2\left(2\right)\\ C_2H_2+2AgNO_3+2NH_3\rightarrow Ag_2C_2+2NH_4NO_3\\ n_{Ag_2C_2}=\dfrac{18}{240}=0,075=n_{C_2H_2}\\ n_{Br_2\left(tổng\right)}=\dfrac{40}{160}=0,25\left(mol\right)\\ n_{Br_2\left(1\right)}=2.n_{C_2H_2}=2.0,075=0,15\left(mol\right)\\ n_{Br_2\left(2\right)}=0,25-0,15=0,1\left(mol\right)\\ V=V_{C_2H_2\left(đktc\right)}+V_{C_2H_4\left(đktc\right)}=0,075.22,4+0,1.22,4=3,92\left(lít\right)\\ Chọn.A\)

bài này rất dễ

a, x=2+24-22-23=0

b,  x=3-3-7=-7

c,   x=11 hoặc -11

d,  x=2

h,   x thuộc N

14. B

19. C

20. A

21. A

22. D

23. B

CÂU :14. B

CÂU:19. C

CÂU:20. A

CÂU:21. A

22. D

23. B

C

c

C. 24 chữ cái.

Đặt A=1 + 2 + 2²+ 2³+ 2⁴ +... + 2⁹⁹ + 2¹⁰⁰

=>2A=2 + 2²+ 2³+ 2⁴ +... + 2⁹⁹ + 2¹⁰⁰+2¹⁰¹

=>2A-A=(2 + 2²+ 2³+ 2⁴ +... + 2⁹⁹ + 2¹⁰⁰+2¹⁰¹)-(1 + 2 + 2²+ 2³+ 2⁴ +... + 2⁹⁹ + 2¹⁰⁰)

=>A=2¹⁰¹-1

41+42+43+44-21-22-23-24

=( 41- 21 )+ (42-22)+(43-23)+(44-24)

=20 + 20 +20 +20

=20 . 4

=80

41+ 42 + 43 + 44 - 21 - 22 - 23 - 24 = 80

41 + 42 + 43 + 44 - 21 - 22 - 23 - 24

= ( 41 - 21 ) + ( 42 - 22 ) + ( 43 - 23 ) + ( 44 - 24 )

= 20 + 20 + 20 + 20

= 80

\(A=1+2+2^2+2^3+2^4+...+2^{99}+2^{100}\)

\(\Rightarrow2A=2+2^2+2^3+2^4+2^5+...+2^{100}+2^{101}\)

\(\Rightarrow2A-A=2^{101}-1\)

\(\Leftrightarrow A=2^{101}-1\)

Đặt biểu thức là A

ta có 2A-A=2^101-1

Đặt \(A=1+2+2^2+2^3+2^4+...+2^{99}+2^{100}\)

\(\Rightarrow2A=2+2^2+2^3+...+2^{100}+2^{101}\)

\(\Rightarrow A=2A-A=\left(2+2^2+2^3+2^4+...+2^{101}\right)-\left(1+2+2^2+2^3+...+2^{100}\right)=2^{101}-1\)