c) x=-2 nha

d) =\(\frac{1}{5.6}\)+\(\frac{1}{6.7}\)+......+\(\frac{1}{11.12}\)

=\(\frac{1}{5}\)-\(\frac{1}{6}\)+\(\frac{1}{6}\)-\(\frac{1}{7}\)+.....+\(\frac{1}{11}\)-\(\frac{1}{12}\)

=\(\frac{1}{5}\)-\(\frac{1}{12}\)= \(\frac{7}{60}\)

bạn ơi kết quả là 7/60

\(=\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{11.12}\)

\(=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{12}\)

\(=\frac{1}{5}-\frac{1}{12}\)

\(=\frac{7}{60}\)

\(A=\frac{1}{4}:\left(10,3-9,8\right)-\frac{3}{4}\)

\(A=\frac{1}{4}:\left(0,5\right)-\frac{3}{4}\)

\(A=\frac{1}{4}:\frac{1}{2}-\frac{3}{4}\)

\(A=\frac{1}{4}\cdot2-\frac{3}{4}=\frac{1}{2}-\frac{3}{4}=\frac{2}{4}-\frac{3}{4}=\frac{-1}{4}\)

Bài 1:

a, \(A=\frac{1}{4}:0,5-\frac{3}{4}\)

       \(=\frac{1}{2}-\frac{3}{4}\)

         \(=\frac{-1}{4}\)

b, \(B=\frac{6}{7}+\frac{5}{8}:5-\frac{3}{16}.\left(-2\right)^2\)

       \(=\frac{6}{7}+\frac{1}{8}-\frac{3}{4}\)

       \(=\frac{6}{7}+\frac{-5}{8}\)

       \(=\frac{13}{56}\)

Hk tốt

\(B=\frac{6}{7}+\frac{5}{8}:5-\frac{3}{16}.\left(-2\right)^2\)

\(B=\frac{6}{7}+\frac{5}{8}\cdot\frac{1}{5}-\frac{3}{16}.4\)

\(B=\frac{6}{7}+\frac{1}{8}-\frac{3}{4}=\frac{55}{56}-\frac{3}{4}=\frac{13}{56}\)

1) \(\left(\frac{7}{8}-\frac{3}{4}\right).1\frac{1}{3}-\frac{2}{7}.\left(3,5\right)^2\)

= \(\frac{1}{8}.\frac{4}{3}-\frac{2}{7}.\frac{49}{4}\) = \(\frac{-10}{3}\)

2) \(\frac{5}{4}:\frac{1}{2}-\frac{3}{4}\) = \(\frac{7}{4}\)

\(\begin{array}{l}a)\left( {\frac{2}{3} + \frac{1}{6}} \right):\frac{5}{4} + \left( {\frac{1}{4} + \frac{3}{8}} \right):\frac{5}{2}\\ = \left( {\frac{4}{6} + \frac{1}{6}} \right).\frac{4}{5} + \left( {\frac{2}{8} + \frac{3}{8}} \right).\frac{2}{5}\\ = \frac{5}{6}.\frac{4}{5} + \frac{5}{8}.\frac{2}{5}\\ = \frac{2}{3} + \frac{1}{4}\\ = \frac{8}{{12}} + \frac{3}{{12}}\\ = \frac{{11}}{{12}}\\b)\frac{5}{9}:\left( {\frac{1}{{11}} - \frac{5}{{22}}} \right) + \frac{7}{4}.\left( {\frac{1}{{14}} - \frac{2}{7}} \right)\\ = \frac{5}{9}:\left( {\frac{2}{{22}} - \frac{5}{{22}}} \right) + \frac{7}{4}.\left( {\frac{1}{{14}} - \frac{4}{{14}}} \right)\\ = \frac{5}{9}:\frac{{ - 3}}{{22}} + \frac{7}{4}.\frac{{ - 3}}{{14}}\\ = \frac{5}{9}.\frac{{ - 22}}{3} + \frac{{ - 3}}{8}\\ = \frac{{ - 110}}{{27}} + \frac{{ - 3}}{8}\\ = \frac{{ - 880}}{{216}} + \frac{{ - 81}}{{216}}\\ = \frac{{ - 961}}{{216}}\end{array}\)

Bài 1:

a) Ta có:

\(3,2\cdot x+\left(-1,2\right)\cdot x+2,7=-4,9\)

\(\Rightarrow\left[3,2+\left(-1,2\right)\right]\cdot x=\left(-4,9\right)-2,7\)

\(\Rightarrow2x=-7,6\)

\(\Rightarrow x=\left(-7,6\right):2\)

\(\Rightarrow x=-3,8\)

Vậy \(x=-3,8\)

b) Ta có:

-5,6.x+2,9.x-3,86=-9,8

=>[(-5,6)+2,9].x=(-9,8)+3,86

=>(-2,7).x=-5,94

=>x=(-5,94):(-2,7)

=>x=2,3

Vậy x=2,2

Dễ mà. ấn máy tính cũng ra

a)

 \(\begin{array}{l}\left( {0,25 - \frac{5}{6}} \right).1,6 + \frac{{ - 1}}{3}\\ =(\frac{25}{100}-\frac{5}{6}).\frac{16}{10}+\frac{-1}{3}\\= \left( {\frac{1}{4} - \frac{5}{6}} \right).\frac{8}{5} + \frac{{ - 1}}{3}\\ = \left( {\frac{6}{{24}} - \frac{{20}}{{24}}} \right).\frac{8}{5} + \frac{{ - 1}}{3}\\ = \frac{{ - 14}}{{24}}.\frac{8}{5} + \frac{{ - 1}}{3}\\ = \frac{{ - 14}}{{15}} + \frac{{ - 1}}{3}\\ = \frac{{ - 14}}{{15}} + \frac{{ - 5}}{{15}}\\ = \frac{{ - 19}}{{15}}\end{array}\)

b)

\(\begin{array}{l}3 - 2.\left[ {0,5 + \left( {0,25 - \frac{1}{6}} \right)} \right]\\ = 3 - 2.\left[ {\frac{1}{2} + \left( {\frac{1}{4} - \frac{1}{6}} \right)} \right]\\ = 3 - 2.\left( {\frac{1}{2} + \frac{1}{{12}}} \right)\\ =3-2.(\frac{6}{12}+\frac{1}{12})\\= 3 - 2.\frac{7}{{12}}\\ = 3 - \frac{7}{6}\\=\frac{18}{6}-\frac{7}{6}\\ = \frac{{11}}{6}\end{array}\)

khó thấy quá bạn ơi