a) \(17.85+15.17+300\\ =17.\left(85+15\right)+300\\ =17.100+300\\ =1700+300\\ =2000\)

b) \(32.39+52.21-12.39+21.48\\ =39.\left(32-12\right)+21.\left(52+48\right)\\ =39.20+21.100\\ =780+2100=2880\)

c) \(175-\left(3.5^2-3^2.5\right)\\ =175-\left(3.25-9.5\right)\\ =175-\left(75-45\right)\\ =175-30=145\)

d) \(99-97+95-93+...+3-1\\ =\left(99-97\right)+\left(95-93\right)+...+\left(3-1\right)\\ =2+2+...+2\\ =2.25=50\)

\(3\left(x-2\right)=-100+211\\ 3\left(x-2\right)=111\\ x-2=37\\ x=39.\)

`#3107.101107`

`3(x - 2) = -100 + 211`

`\Rightarrow 3(x - 2) = 111`

`\Rightarrow x - 2 = 111 \div 3`

`\Rightarrow x - 2 = 37`

`\Rightarrow x = 37 + 2`

`\Rightarrow x = 39`

Vậy, `x = 39.`

\(\dfrac{11}{2}-x:\dfrac{1}{2}=\dfrac{1}{4}\\ x:\dfrac{1}{2}=\dfrac{11}{2}-\dfrac{1}{4}\\ x:\dfrac{1}{2}=\dfrac{21}{4}\\ x=\dfrac{21}{4}.\dfrac{1}{2}\\ x=\dfrac{21}{8}\)

Vậy x = \(\dfrac{21}{8}\)

11/2-x:1/2=1/4

  x : 1/2      = 11/2 - 1/4

  x : 1/2       = 21/4

  x                = 21/4 x 1/2

  x                = 21/8

11/2-x:1/2=1/4

`11/2 - x ÷ 1/2 = 1/4`

`             x ÷ 1/2 = 11/2 - 1/4`

`             x ÷ 1/2 = 21/4`

`             x             = 21/4 × 1/2`

`             x             = 21/8`

25/13 × 17/19 - 17/19 × 1/13 + 24/13 × 2/19

= (25/13 - 1/13) × 17/19 + 24/13 × 2/19

= 24/13 × 17/19 + 24/13 × 2/19

= 24/13 × (17/19 + 2/19)

= 24/13 × 1

= 24/13

@Phạm Lê Minh Vương Bạn copy phải ghi Tk

Tk = Tham khảo

Và bạn là Chiến Binh yêu cầu không phạm luật của Olm!

Trân trọng!

$450-2\times x=75:5-5$

$\Rightarrow 450-2\times x=15-5$

$\Rightarrow 450-2\times x=10$

$\Rightarrow 2\times x=450-10$

$\Rightarrow 2\times x=440$

$\Rightarrow x=440:2$

$\Rightarrow x=220$

450 - 2 x X = 15 - 5

450 - 2 x X =10

         2 x X = 450 - 10

         2 x X = 440

              X = 440 : 2

              X = 220

\(Q=\dfrac{\dfrac{1}{2021}+\dfrac{1}{2022}-\dfrac{1}{2023}}{\dfrac{5}{2021}+\dfrac{5}{2022}-\dfrac{5}{2023}}-\dfrac{\dfrac{2}{2021}+\dfrac{2}{2022}-\dfrac{2}{2023}}{\dfrac{3}{2021}+\dfrac{3}{2022}-\dfrac{3}{2023}}\)

\(=\dfrac{\dfrac{1}{2021}+\dfrac{1}{2022}-\dfrac{1}{2023}}{5\left(\dfrac{1}{2021}+\dfrac{1}{2022}-\dfrac{1}{2023}\right)}-\dfrac{2\left(\dfrac{1}{2021}+\dfrac{1}{2022}-\dfrac{1}{2023}\right)}{3\left(\dfrac{1}{2021}+\dfrac{1}{2022}-\dfrac{1}{2023}\right)}\)

\(=\dfrac{1}{5}-\dfrac{2}{3}=-\dfrac{7}{15}\)

gấp ạ!!

Số tự nhiên lớn nhất có bốn chữ số mà trong đó không có hai chữ số nào giống nhau là: 9876

9876

Ta có: \(E=\dfrac{1}{3}+\dfrac{2}{3^2}+\dfrac{3}{3^3}+...+\dfrac{100}{3^{100}}\)

\(3E=1+\dfrac{2}{3}+\dfrac{3}{3^2}+...+\dfrac{100}{3^{99}}\)

\(3E-E=\left(1+\dfrac{2}{3}+\dfrac{3}{3^2}+..+\dfrac{100}{3^{99}}\right)-\left(\dfrac{1}{3}+\dfrac{2}{3^2}+\dfrac{3}{3^3}+...+\dfrac{100}{3^{100}}\right)\)

\(2E=1+\dfrac{1}{3}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{99}}-\dfrac{100}{3^{100}}\)

\(6E=3+1+\dfrac{1}{3^2}+...+\dfrac{1}{3^{98}}-\dfrac{100}{3^{99}}\)

\(6E-2E=\left(3+1+\dfrac{1}{3^2}+...+\dfrac{1}{3^{98}}-\dfrac{100}{3^{99}}\right)-\left(1+\dfrac{1}{3}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{99}}-\dfrac{100}{3^{100}}\right)\)

\(4E=3-\dfrac{100}{3^{99}}-\dfrac{100}{3^{100}}\)

\(\Rightarrow E=\dfrac{3-\dfrac{100}{3^{99}}-\dfrac{100}{3^{100}}}{4}=\dfrac{3}{4}-\dfrac{\dfrac{100}{3^{99}}+\dfrac{100}{3^{100}}}{4}< \dfrac{3}{4}\) (đpcm)

đỀ LỖI 

cho mình hỏi đề lỗi ở chỗ nào ạ?