Cộng, trừ, nhân, chia số hữu tỉ

\(\frac{2}{3} - \frac{{ - 3}}{7} = \frac{2}{3} + \frac{3}{7} = \frac{{14}}{{21}} + \frac{9}{{21}} = \frac{{23}}{{21}}\)

\(\frac{{ - 2}}{3} + \frac{2}{5}:\frac{{ - 3}}{5} = \frac{{ - 2}}{3} + \frac{2}{5}.\frac{{ - 5}}{3} = \frac{{ - 2}}{3} + \frac{{ - 2}}{3} = \frac{{ - 4}}{3}\)

Ta có $\dfrac{5}{{11}}:\dfrac{{15}}{{22}}$\( = \dfrac{5}{{11}}.\dfrac{{22}}{{15}} = \dfrac{{5.22}}{{11.15}} = \dfrac{2}{3}\)

Ta có:

\(\dfrac{2}{3} + \dfrac{5}{4} = \dfrac{8}{{12}} + \dfrac{{15}}{{12}} = \dfrac{{23}}{{12}}.\)

\(\dfrac{1}{6} + \dfrac{3}{2} = \dfrac{1}{6} + \dfrac{9}{6} = \dfrac{{10}}{6} = \dfrac{5}{3}.\)

\(\dfrac{5}{3} + \dfrac{3}{2} = \dfrac{{10}}{6} + \dfrac{9}{6} = \dfrac{{19}}{6}.\)

\(1 + \dfrac{{13}}{{12}} = \dfrac{{12}}{{12}} + \dfrac{{13}}{{12}} = \dfrac{{25}}{{12}}.\)

Do đó \(\dfrac{{23}}{{12}}\) là kết quả của phép tính: \(\dfrac{2}{3} + \dfrac{5}{4}.\)

\(\begin{array}{l}3\frac{1}{2} - \frac{2}{3}:\frac{5}{{ - 3}} - 0,3\\ = \frac{7}{2} - \frac{2}{3}.\frac{{ - 3}}{5} - \frac{3}{{10}}\\ = \frac{7}{2} - \frac{{ - 2}}{5} - \frac{3}{{10}}\\ = \frac{7}{2} + \frac{2}{5} - \frac{3}{{10}}\\ = \frac{{35}}{{10}} + \frac{4}{{10}} - \frac{3}{{10}}\\ = \frac{{36}}{{10}}\\ = \frac{{18}}{5}\\ = 3\frac{3}{5}\end{array}\)

\(\begin{array}{l} - 0,12 - 2x =  - 1\frac{2}{5}\\ \Leftrightarrow \frac{{ - 12}}{{100}} - 2x = \frac{{ - 7}}{5}\\ \Leftrightarrow \frac{{ - 3}}{{25}} - 2x = \frac{{ - 7}}{5}\\ \Leftrightarrow 2x = \frac{{ - 3}}{{25}} - (\frac{{ - 7}}{5})\\ \Leftrightarrow 2x = \frac{{ - 3}}{{25}} + \frac{{35}}{{25}}\\ \Leftrightarrow 2x = \frac{{32}}{{25}}\\ \Leftrightarrow x = \frac{{32}}{{25}}:2\\ \Leftrightarrow x = \frac{{32}}{{25}}.\frac{1}{2}\\ \Leftrightarrow x = \frac{{16}}{{25}}\end{array}\)

Ta có \(1\dfrac{4}{5}:\left( { - \dfrac{3}{4}} \right)\)\( = \dfrac{9}{5}.\left( { - \dfrac{4}{3}} \right) =  - \dfrac{{9.4}}{{5.3}} =  - \dfrac{{12}}{5}\)

$\dfrac{2}{7} + \left( {\dfrac{{ - 3}}{5}} \right) + \dfrac{3}{5} = \dfrac{2}{7} + \left[ {\left( {\dfrac{{ - 3}}{5}} \right) + \dfrac{3}{5}} \right]$$ = \dfrac{2}{7} + 0\, = \dfrac{2}{7}.$

\(M = \dfrac{{11}}{{20}}.68 - 4,2.2022 + 4\dfrac{1}{5}.2022 \)\(- 68.( - 0,45)\)\( = 0,55.68 - 4,2.2022 + 4,2.2022 \)\(+ 68.0,45\)\( = (0,55.68 + 68.0,45) \)\(+ ( - 4,2.2022 + 4,2.2022)\)\(= 68.(0,55 + 0,45) + 0\)\( = 68.1\\ = 68\)

\(\begin{array}{l}\frac{{x + \frac{3}{2}}}{6} = \frac{{ - 5}}{{12}}\\ \Leftrightarrow \frac{{2.(x + \frac{3}{2})}}{{12}} = \frac{{ - 5}}{{12}}\\ \Leftrightarrow \frac{{2x + 3}}{{12}} = \frac{{ - 5}}{{12}}\\ \Leftrightarrow 2x + 3 =  - 5\\ \Leftrightarrow 2x =  - 5 - 3\\ \Leftrightarrow 2x =  - 8\\ \Leftrightarrow x =  - 4\end{array}\)

Vậy x = -4

Ta có \(\dfrac{2}{3}x =  - \dfrac{1}{{8}}\)

\(x = \left( { - \dfrac{1}{{8}}} \right):\dfrac{2}{3}\)

\(x = \dfrac{{ - 1}}{8}.\dfrac{3}{2}\)

\(x =  - \dfrac{3}{{16}}\)

Vậy \(x =  - \dfrac{3}{{16}}.\)

Ta có \(\dfrac{2}{5} + \left( { - \dfrac{4}{3}} \right) + \left( { - \dfrac{1}{2}} \right)\)\( = \dfrac{{12}}{{30}} + \left( {\dfrac{{ - 40}}{{30}}} \right) + \left( {\dfrac{{ - 15}}{{30}}} \right) = \dfrac{{12 - 40 - 15}}{{30}} = \dfrac{{ - 43}}{{30}}\)

Ta có:

\(\begin{array}{l}\frac{{\frac{3}{{11}} + \frac{3}{{17}} - \frac{3}{{23}} + \frac{3}{{29}}}}{{\frac{7}{{11}} + \frac{7}{{17}} - \frac{7}{{23}} + \frac{7}{{29}}}}\\ = \frac{{3.(\frac{1}{{11}} + \frac{1}{{17}} - \frac{1}{{23}} + \frac{1}{{29}})}}{{7.(\frac{1}{{11}} + \frac{1}{{17}} - \frac{1}{{23}} + \frac{1}{{29}})}}\\ = \frac{3}{7}\end{array}\)

Ta xét 2 trường hợp sau:

+ Trường hợp 1:

\[\left\{ {_{x - 1 > 0}^{2x + 7 < 0}} \right. \Leftrightarrow \left\{ {_{x > 1}^{2x <  - 7}} \right. \Leftrightarrow \left\{ {_{x > 1}^{x < \frac{{ - 7}}{2}}} \right.\] ( Vô lí)

+ Trường hợp 2:

\[\left\{ {_{x - 1 < 0}^{2x + 7 > 0}} \right. \Leftrightarrow \left\{ {_{x < 1}^{2x >  - 7}} \right. \Leftrightarrow \left\{ {_{x < 1}^{x > \frac{{ - 7}}{2}}} \right. \Leftrightarrow \frac{{ - 7}}{2} < x < 1\]

Mà x nguyên

\( \Rightarrow x \in \{  - 3; - 2; - 1;0\} \)

Vậy có 4 giá trị của x thỏa mãn

Ta có \(\dfrac{5}{7}:x - \dfrac{2}{5} = \dfrac{1}{3}\)

\(\dfrac{5}{7}:x = \dfrac{1}{3} + \dfrac{2}{5}\)

\(\dfrac{5}{7}:x = \dfrac{5}{{15}} + \dfrac{6}{{15}}\)

\(\dfrac{5}{7}:x = \dfrac{{11}}{{15}}\)

\(x = \dfrac{5}{7}:\dfrac{{11}}{{15}}\)

\(x = \dfrac{5}{7}.\dfrac{{15}}{{11}}\)

\(x = \dfrac{{75}}{{77}}\)

Vậy \({x_0} = \dfrac{{75}}{{77}} < \dfrac{{77}}{{77}} = 1\) .

\(\dfrac{2}{{11}} - \dfrac{5}{{13}} + \dfrac{9}{{11}} - \dfrac{8}{{13}} = \left( {\dfrac{2}{{11}} + \dfrac{9}{{11}}} \right) - \left( {\dfrac{5}{{13}} + \dfrac{8}{{13}}} \right) = \dfrac{{11}}{{11}} - \dfrac{{13}}{{13}} = 1 - 1 = 0.\)

\(\begin{array}{l}(\frac{1}{3} - 1).(\frac{1}{4} - 1)....(\frac{1}{{2022}} - 1)\\ = \frac{{ - 2}}{3}.\frac{{ - 3}}{4}.....\frac{{ - 2021}}{{2022}}\\ = \frac{2}{{2022}}\\ = \frac{1}{{1011}}\end{array}\)

Lời giải

Đặt $Q =  P – 3  = 3 + 30 + 33 + 36 +…+ 3300 – 3 = 30 + 33 + 36 +…+ 3300$

Số số hạng của tổng Q là:

\[\dfrac{{3300 - 30}}{3} + 1 = 1091\]

Tổng Q là: \(\dfrac{{(3300 + 30).1091}}{2} = 1816515\)

Ta được  $5x = 1816515$

Do đó:$ x = 1816515 : 5 = 363 303$

Ta có \(P = \left( {\dfrac{{ - 3}}{4} + \dfrac{2}{5}} \right):\dfrac{3}{7} + \left( {\dfrac{3}{5} + \dfrac{{ - 1}}{4}} \right):\dfrac{3}{7}\)$ = \left( {\dfrac{{ - 3}}{4} + \dfrac{2}{5} + \dfrac{3}{5} + \dfrac{{ - 1}}{4}} \right):\dfrac{3}{7}$

\( = \left[ {\left( {\dfrac{{ - 3}}{4} + \dfrac{{ - 1}}{4}} \right) + \left( {\dfrac{2}{5} + \dfrac{3}{5}} \right)} \right]:\dfrac{3}{7}\) \( = \left( { - 1 + 1} \right):\dfrac{3}{7} = 0:\dfrac{3}{7} = 0\)

Vậy \(P = 0.\)

$\left( { - 2 - \dfrac{1}{3} - \dfrac{1}{5}} \right) - \left( {\dfrac{2}{3} - \dfrac{6}{5}} \right) = ( - 2) + \left( { - \dfrac{1}{3} - \dfrac{2}{3}} \right) + \left( { - \dfrac{1}{5} + \dfrac{6}{5}} \right)$$ = ( - 2) + ( - 1) + 1 =  - 2$