a: =(1-2-3+4)+(5-6-7+8)+...+(21-22-23+24)

=0+0+...+0

=0

b: =-7111+53+711-153=-6400-100=-6500

c: =-43(-1-296+296)=-43*(-1)=43

1.a,=(54+45+1).113

=100.113

=11300

b,=(3/7+8/14)+(4/9+10/18)

=1+1

=2

2.a,=13/10+1/3

=49/30

b,=12/9.(1/12+1/6)

=12/9.1/4

=1/3

c,=3/4.3/2

=9/8

d,=3/2-1/3

=7/6

1:tính bằng cách thuận tiện nhất:

a)54 x 113 + 45 x 113 + 113

= 54 x 113 + 45 x 113 + 113x1

=113 x(54+45+1)

= 113x100

=1300

 b)3/7 + 4/9 + 8/14 + 10/18

=(3/7+8/14)+(4/9+10/18)

=    1           + 1

=2

k) 4 x 113 x 25 - 5 x 112 x 20

= (4 x 25) x 113 - (5 x 20) x 112

= 100 x 113 - 100 x 112

= 100 x (113 - 112)

= 100

p) 1235 x 6789 x (630 - 315 x 2) : 1996

= 1235 x 6789 x (630 - 630) : 1996

= 1235 x 6789 x 0 : 1996

= 0

l) 54 x 113 + 45 x 113 + 113

= 113 (54 + 45 + 1)

= 113 x 100

= 11300

u) (500 x 9 - 250 x 18) x (1 + 2 + 3 + ... + 9)

= (2 x 250 x 9 - 250 x 2 x 9) x (1 +2 + 3 + ... + 9)

= 0 x (1 + 2 + 3 + ... + 9)

= 0

Baì này dễ quá

a,

= 113 x (54 + 45 + 1)

= 113 x 100

= 11300

b,

= 7/10 x (3 + 5 + 2)

= 7/10 x 10

= 7

11300

7

a, 54 x 113 + 45 x 113 + 113

= 113 x ( 54+45+1)

= 113 x 100

= 11300

b, 3 x 7/10 + 7/10 x 5 + 2 x 14/20

= 7/10 + ( 3+5+2)

= 7/10 x 10

= 7

2)\(x\left(x+1\right)\left(x+2\right)\left(x+3\right)=[x\left(x+3\right)].\left[\left(x+1\right)\left(x+2\right)\right]=\left(x^2+3x\right)\left(x^2+3x+2\right)\)

Đặt y=\(x^2+3x\) ta được:\(y\left(y+2\right)=y^2+2y=\left(y+1\right)^2-1\)

Vậy GTNN của x(x+1)(x+2)(x+3) là -1

bài 4

\(\left\{{}\begin{matrix}a+b=170\\\left[{}\begin{matrix}\dfrac{2}{5}a+\dfrac{1}{2}b=21\left(1\right)\\\dfrac{1}{2}a+\dfrac{2}{5}b=21\left(2\right)\end{matrix}\right.\end{matrix}\right.\)

\(\left[{}\begin{matrix}\dfrac{2}{5}a+\dfrac{1}{2}b=\dfrac{4\left(a+b\right)+b}{10}=21\Rightarrow b=210-4.170=-470\\\dfrac{1}{2}a+\dfrac{2}{5}b=\dfrac{4\left(a+b\right)+a}{10}=21\Rightarrow210-4.170=-470\end{matrix}\right.\)

\(470+170=640\)

Đáp số 640

4)Gọi hai số đó là a và b

\(a+b=170\Rightarrow a=170-b\\ \dfrac{1}{2}a+\dfrac{2}{5}b=21\Leftrightarrow\dfrac{1}{2}\left(170-b\right)+\dfrac{2}{5}b=21\Leftrightarrow-\dfrac{1}{10}b=-64\Leftrightarrow b=640;a=170-640=-470\)

d,155-10(x+1)=55

          10(x+1) = 155 - 55

          10(x+1) = 100

               x+1  = 100 : 10

               x+1  = 10

                x     = 10 - 1 =9

e,6(x+\(2^3\))+40=100

6(x+\(2^3\))         = 100 - 40

6(x+\(2^3\))         = 60

    (x+\(2^3\))       = 60 : 6

(x+\(2^3\))           = 10

x                       = 10 - \(2^3\)

x                       = 10 - 8 = 2

f,\(2^2\)(x+\(3^2\))-5=55

\(2^2\)(x+\(3^2\))     = 55 + 5

\(2^2\)(x+\(3^2\))     = 60

        (x+\(3^2\))    = 60 : \(2^2\)

          (x+\(3^2\))  = 60 : 4

         (x+\(3^2\))   = 15

         x + 9         = 15

         x               = 15-9=6.

Hok tốt !

d) \(155-10\left(x+1\right)=55\)

\(\Rightarrow10\left(x+1\right)=155-55\)

\(\Rightarrow10\left(x+1\right)=100\)

\(\Rightarrow x+1=100:10\)

\(\Rightarrow x+1=10\)

\(\Rightarrow x=10-1\)

\(\Rightarrow x=9\)

Vậy x = 9

e) \(6\left(x+2^3\right)+40=100\)

\(\Rightarrow6\left(x+2^3\right)=100-40\)

\(\Rightarrow6\left(x+2^3\right)=60\)

\(\Rightarrow x+2^3=60:6\)

\(\Rightarrow x+2^3=10\)

\(\Rightarrow x+8=10\)

\(\Rightarrow x=10-8\)

\(\Rightarrow x=2\)

Vậy x = 2

f) \(2^2\left(x+3^2\right)-5=55\)

\(\Rightarrow2^2\left(x+3^2\right)=55+5\)

\(\Rightarrow2^2\left(x+3^2\right)=60\)

\(\Rightarrow4\left(x+9\right)=60\)

\(\Rightarrow x+9=60:4\)

\(\Rightarrow x+9=15\)

\(\Rightarrow x=15-9\)

\(\Rightarrow x=6\)

Vậy x = 6

\(d,155-10\left(x+1\right)=55\)                                               \(e,6\left(x+2^3\right)+40=100\)

\(\Rightarrow10\left(x+1\right)=155-55\)                                            \(\Rightarrow\left(x+2^3\right)+40=100:6\)

\(\Rightarrow10\left(x+1\right)=100\)                                                         ủa hình như câu này sai đề thì phải ??-.-'''

\(\Rightarrow x+1=100:10\)

\(\Rightarrow x+1=10\)

\(\Rightarrow x=10-1=9\)

e: =>x=0 hoặc x=1

a:565-13.x=30

13.x=565-370

13.x=195

x=195:13

x=15

Nếu sai sót gì thì e xin lỗi ạ ^^