a) (-15)+ 7. (-3)

=-15-21=-36

b) 21.(17-34)-22.(-15)

=21.(-17)+330=-357+330=-27

c) (-15).(-37)+(-6).9

=555-54=501

d) (-27).(-58)-(-14).8

=1566+112=1678

a) (-15)+ 7. (-3)

=(-15)+ (-21)=-36

b)21.(17-34)-22.(-15)

=21.(-17)-(-330)=(-357)-(-330)=-27

c) (-15).(-37)+(-6).9

=555+(-54)=501

d) (-27).(-58)-(-14).8

=1566-(-112)=1678

a) (-15) + 7.(-3)

= (-15) + (-21)

= -36.

b) 21.(17 - 34) - 22.(-15)

= 21.(-17) - (-330)

= 21.(-17) + 330

= (-357) + 330

= -27.

c) (-15).(-37) + (-6).9

= 555 + (-54)

= 501.

d) (-27).(-58) - (-14).8

= (-27).(-58) + 14.8

= 1566 + 112

= 1678.

BÀI 1

a,  \(5\times\frac{-7}{10}=\frac{-35}{10}=\frac{-7}{2}\)

b,  \(\frac{4}{5}\times\frac{-7}{10}=\frac{-28}{50}=\frac{-14}{25}\)

c,  \(\frac{4}{9}+\frac{4}{3}\times\frac{16}{4}=\frac{4}{9}+\frac{16}{3}=\frac{52}{9}\)

d,  \(\frac{11}{22}-\frac{3}{9}\times\frac{14}{21}=\frac{11}{22}-\frac{2}{9}=\frac{55}{198}=\frac{5}{18}\)  

BÀI 2

\(A=\frac{6}{13}\times\frac{5}{7}+\frac{6}{13}\times\frac{2}{7}+\frac{17}{13}\)

\(A=\frac{30}{91}+\frac{12}{91}+\frac{17}{13}\)

\(A=\frac{30}{91}+\frac{12}{91}+\frac{119}{91}\)

\(A=\frac{161}{91}=\frac{23}{13}\)

\(B=\frac{11}{15}\times\frac{4}{11}+\frac{11}{15}\times\frac{5}{11}+\frac{11}{15}\times\frac{2}{11}\)

\(B=\frac{4}{15}+\frac{1}{3}+\frac{2}{15}\)

\(B=\frac{11}{15}\)

\(C=\left(\frac{19}{64}-\frac{33}{22}+\frac{24}{51}\right)\times\left(\frac{1}{5}-\frac{1}{15}-\frac{2}{15}\right)\)

\(C=\frac{-797}{1088}\times0\)

\(C=0\)

\(D=\frac{8}{13}\times\frac{7}{12}+\frac{8}{13}\times\frac{5}{12}-\frac{1}{12}\)

\(D=\frac{14}{39}+\frac{10}{39}-\frac{1}{12}\)

\(D=\frac{83}{156}\)

bạn biết câu náy không (24 + 11) . {546 - [14 . (64 - 2^{3}3) : 2]} =

Câu 3:

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

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

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

\(2A=3^{101}-3\) 

Mà: \(2A+3=3^N\)

\(\Rightarrow3^{101}-3+3=3^N\)

\(\Rightarrow3^{101}=3^N\)

\(\Rightarrow N=101\)

Vậy: ... 

Câu 1:

\(A=4+2^2+...+2^{20}\)

Đặt \(B=2^2+2^3+...+2^{20}\)

=>\(2B=2^3+2^4+...+2^{21}\)

=>\(2B-B=2^3+2^4+...+2^{21}-2^2-2^3-...-2^{20}\)

=>\(B=2^{21}-4\)

=>\(A=B+4=2^{21}-4+4=2^{21}\) là lũy thừa của 2

Câu 6:

Đặt A=1+2+3+...+n

Số số hạng là \(\dfrac{n-1}{1}+1=n-1+1=n\left(số\right)\)

=>\(A=\dfrac{n\left(n+1\right)}{2}\)

=>\(A⋮n+1\)

Câu 5:

\(A=5+5^2+...+5^8\)

\(=\left(5+5^2\right)+\left(5^3+5^4\right)+\left(5^5+5^6\right)+\left(5^7+5^8\right)\)

\(=\left(5+5^2\right)+5^2\left(5+5^2\right)+5^4\left(5+5^2\right)+5^6\left(5+5^2\right)\)

\(=30\left(1+5^2+5^4+5^6\right)⋮30\)

giúp mik với 

\(A=2^0+2^1+2^2+...+2^{59}\)

\(=2^0\left(1+2+2^2\right)+2^3\left(1+2+2^2\right)+...+2^{57}\left(1+2+2^2\right)\)

\(=2^0.7+2^3.7+...+2^{57}.7\)

\(=7\left(2^0+2^3+...+2^{57}\right)⋮7\)

Số số hạng của A:

90 - 1 + 1 = 90 (số)

Do 90 chia hết cho 3 nên có thể nhóm thành nhóm 3 số hạng

Ta có:

A = 2¹ + 2² + 2³ + ... + 2⁹⁰

= (2 + 2² + 2³) + (2⁴ + 2⁵ + 2⁶) + ... + (2⁸⁸ + 2⁸⁹ + 2⁹⁰)

= 2.(1 + 2 + 2²) + 2⁴.(1 + 2 + 2²) + ... + 2⁸⁸.(1 + 2 + 2²)

= 2.7 + 2⁴.7 + ... + 2⁸⁸.7

= 7.(2 + 2⁴ + ... + 2⁸⁸) ⋮ 7

Vậy A ⋮ 7

b) A = 2¹ + 2² + 2³ + ... + 2⁹⁰

⇒ 2A = 2² + 2³ + 2⁴ + ... + 2⁹¹

⇒ A = 2A - A = (2² + 2³ + 2⁴ + ... + 2⁹¹) - (2 + 2² + 2³ + ... + 2⁹⁰)

= 2⁹¹ - 2

c) \(55-7.\left(x+3\right)=6\)

\(7.\left(x+3\right)=55-6\)

\(7.\left(x+3\right)=49\)

\(x+3=49:7\)

\(x+3=7\)

\(x=7-3\)

\(x=4\)

d) \(-14-x+\left(-15\right)=-10\)

\(-29-x=-10\)

\(x=-29+10\)

\(x=-19\)

-----------------------------

Số số hạng của A:

\(60-1+1=60\) (số)

Do \(60⋮6\) nên ta có thể nhóm các số hạng của A thành từng nhóm mà mỗi nhóm có 6 số hạng như sau:

\(A=\left(2+2^2+2^3+2^4+2^5+2^6\right)+\left(2^7+2^8+2^9+2^{10}+2^{11}+2^{12}\right)+...+\left(2^{55}+2^{56}+2^{57}+2^{58}+2^{59}+2^{60}\right)\)

\(=2.\left(1+2+2^2+2^3+2^4+2^5\right)+2^7.\left(1+2+2^2+2^3+2^4+2^5\right)+...+2^{55}.\left(1+2+2^2+2^3+2^4+2^5\right)\)

\(=2.63+2^7.63+...+2^{55}.63\)

\(=63.\left(2+2^7+...+2^{55}\right)\)

\(=21.3.\left(2+2^7+...+2^{55}\right)⋮21\)

Vậy \(A⋮21\)

55-7(x+3)=6

7(x+3)=55-6=49

(x+3)=49:7=7

x=7-3=4

(-14)-x + (-15)=-10

(-14)-x=-10-15=-25

x           =-14-25=-39 

A chia hết 31 chứ

a: -3/4x12=-36/4=-9

b: \(=\dfrac{7}{15}\cdot\dfrac{10}{21}=\dfrac{7}{21}\cdot\dfrac{10}{15}=\dfrac{1}{3}\cdot\dfrac{2}{3}=\dfrac{2}{9}\)

c: \(=\dfrac{7}{18}\cdot\dfrac{12}{21}=\dfrac{12}{18}\cdot\dfrac{7}{21}=\dfrac{2}{3}\cdot\dfrac{1}{3}=\dfrac{2}{9}\)

d: \(=\dfrac{11}{15}\cdot\dfrac{5}{22}=\dfrac{11}{22}\cdot\dfrac{5}{15}=\dfrac{1}{2}\cdot\dfrac{1}{3}=\dfrac{1}{6}\)

e: \(=-\dfrac{8}{15}\cdot\dfrac{5}{4}=\dfrac{-40}{60}=\dfrac{-2}{3}\)

f: \(=-15\cdot\dfrac{3}{5}=-9\)

`#` `\text{dkhanhqlv}`

`4)`

`a)3.(-5/11)`

`=-15/11`

`b)3/5+4/7 . 14/6`

`=3/5 + 4/3`

`=9/15+20/15`

`=29/15`

`c) 10/21-3/8 . 4/15`

`=10/21-1/10`

`=100/210-21/210`

`=79/100`

`d)(2/3+3/4)(5/7+5/14)`

`=(8/12+9/12)(10/14+5/14)`

`=17/12 . 15/14`

`=85/56`

`5)`

`a)x-1/2=3/10 . 5/6`

`=>x-1/2=1/4`

`=>x=1/4+1/2`

`=>x=1/4+2/4`

`=>x=3/4`

`b)x/5 = -3/14`

`=>x : 5 = -3/14`

`=>x=-3/14 . 5`

`=>x=-15/14`

`c)x+2/3=9/15 . 5/27`

`=>x+2/3=1/9`

`=>x=1/9-2/3`

`=>x=1/9-6/9`

`=>x=-5/9`

a. ( 23 - 21) + ( 19 - 17) + ( 15 - 13) + ( 11 - 9) + ( 7 - 5) + ( 3 - 1) 

= 2 + 2 + 2 + 2 + 2 + 2 

= 2 x 6

= 12

b. ( 24 - 22 ) + ( 20 - 18 ) + ( 16 - 14 ) + ( 12 - 10) + ( 8 - 6 ) + ( 4 - 2) 

= 2 + 2 + 2 + 2 + 2 + 2 

= 2 x 6 

= 12