Lời giải:
a.

$A=32.7^2-22.7^2+90.7^2+25.4.51$

$=7^2(32-22+90)+100.51=49.100+100.51=100(49+51)=100.100=10000$

b.

\(X=\frac{1}{2.6}+\frac{1}{4.9}+\frac{1}{6.12}+...+\frac{1}{36.57}+\frac{1}{438.60}\\ =\frac{1}{(1.2).(2.3)}+\frac{1}{(2.2).(3.3)}+\frac{1}{(3.2)(4.3)}+...+\frac{1}{(18.2)(19.3)}+\frac{1}{(19.2).(20.3)}\)

\(=\frac{1}{2.3}(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{18.19}+\frac{1}{19.20})\)

$=\frac{1}{2.3}(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{19}-\frac{1}{20})$

$=\frac{1}{6}(1-\frac{1}{20})=\frac{19}{120}$

$B=2023-X=2023-\frac{19}{120}=2022\frac{101}{120}$

c/

$C=1+2023+2023^2+2023^3+...+2023^{2022}+2023^{2023}$

$2023C=2023+2023^2+2023^3+2023^4+...+2023^{2023}+2023^{2024}$

$\Rightarrow 2023C-C=2023^{2024}-1$

$\Rightarrow C=\frac{2023^{2024}-1}{2023}< 2023^{2024}-1$

$\Rightarrow C< D$

= \(7^2\left(32.22+90\right)+\left(25.4\right).51\)

= \(7^2.100+100.51\)

= \(49.100+100.51\)

= \(100.\left(49+51\right)\)

= 100.100

= 10000

/ là J vậy bạn

giúp tui với

a) -2/5 + 1/4       b) 8/9 : -2/3

= -8/20 + 5/20    = 8/9 . 3/-2

= 3/20                 = -2

c) (-7,2) x 19,2 + 80,8 x (-7,2) 

= (-7,2 ) x (19, 2 + 80,8)

= - 7,2 x 100

= -72

d) [2\(\dfrac{1}{4}\) x (-4) ] + 1/2 : [75% - 10/3]

= [9/4 x (-4) ] + 1/2 : [75% - 10/3]

= -9 + 1/2 : -2,5

= -9 + 0,5 : -2,5

= -9 + -0,2

= -9,2

a, \(\dfrac{-2}{5}+\dfrac{1}{4}=\dfrac{-8}{20}+\dfrac{5}{20}=\dfrac{-3}{20}\)

b, \(\dfrac{8}{9}\div\dfrac{-2}{3}=\dfrac{8}{9}\times\dfrac{-3}{2}=\dfrac{-4}{3}\)

c, \(\left(-7,2\right)\times19,2+80,8\times\left(-7,2\right)\)

\(=\left(-7,2\right)\times\left(19,2+80,8\right)\)

\(=\left(-7,2\right)\times100=-720\)

d, \(\left[2\dfrac{1}{4}\times\left(-4\right)\right]+\dfrac{1}{2}\div\left[75\%-\dfrac{10}{3}\right]\)

=\(\left[\dfrac{9}{4}\times\left(-4\right)\right]+\dfrac{1}{2}\div\left[\dfrac{75}{100}-\dfrac{10}{3}\right]\)

\(=-9+\dfrac{1}{2}\div\dfrac{\left(-31\right)}{12}\) 

\(=-9+\dfrac{1}{2}\times\dfrac{\left(-12\right)}{31}\)

\(=-9+\dfrac{-6}{31}=-\dfrac{285}{31}\)

Lời giải:

$x-25\text{%}x-\frac{1}{2}=\frac{-5}{4}$

$x-0,25x=\frac{1}{2}-\frac{5}{4}$

$x(1-0,25)=\frac{-3}{4}$

$x.0,75=\frac{-3}{4}$

$x=\frac{-3}{4}: 0,75=\frac{-3}{4}: \frac{3}{4}=-1$

x - 25% .x - 1/2 = -5/4

x - 1/4 . x - 1/2 = -5/4

(x.x ) - (1/4 - 1/2) = -5/4

2x     - -1/4           = -5/4

2x + 1/4               = -5/4

2x                        = -5/4 - 1/4

2x                        =  -3/2

  x                        = -3/2 : 2 ( -3/2 x 1/2)

  x                        = -3/4

Hỏi gì vậy bn'

Lời giải:
a.

$-2> -19\Rightarrow \frac{-2}{7}> \frac{-19}{7}$

b.

Hỗn số là $5\frac{1}{3}$

c.

$5,8580321\approx 5,86$

a) -2/7 lớn hơn -19/7.
b) Trong số 0,25; 5 1/3; -4/9, chỉ có 5 1/3 là hỗn số.
c) Số 5,8580321 làm tròn đến chữ số thập phân thứ hai là 5,86.

Lời giải:

$\frac{-7}{12}< x-\frac{1}{4}< \frac{2}{3}$

$\Rightarrow \frac{-7}{12}+\frac{1}{4}< x< \frac{2}{3}+\frac{1}{4}$

$\Rightarrow \frac{-1}{3}< x< \frac{11}{12}$

Do $x$ nguyên nên $x=0$

-7/12 < x < -1/4 < 2/3

-7/12 < x < -3/12 < 8/12

 = > x ϵ {-6/12 ; -5/12 ; -4/12}