bài 2 : 

a) số đó là : 

\(7,2:\frac{2}{3}=10,8\)

b) số đó là : 
\(-5:\frac{10}{7}=-3,5\)
 

bài 1 : 

a) \(\frac{8}{10}-\frac{9}{12}+\frac{15}{18}-\frac{12}{14}=\frac{4}{5}-\frac{3}{4}+\frac{5}{6}-\frac{6}{7}=\frac{16}{20}-\frac{15}{20}+\frac{35}{42}-\frac{36}{42}=\frac{1}{20}-\frac{1}{42}=\frac{11}{420}\)

b) \(\frac{5}{7}.\frac{5}{11}+\frac{5}{7}.\frac{2}{11}-\frac{5}{7}.\frac{14}{11}=\frac{5}{7}\left(\frac{5}{11}+\frac{2}{11}-\frac{14}{11}\right)=\frac{5}{7}.-\frac{7}{11}=-\frac{5}{11}\)

c) \(\left(\frac{202}{909}+\frac{333}{444}\right).x=\frac{35}{36}\)

\(\frac{35}{36}x=\frac{35}{36}\)

\(x=\frac{35}{36}:\frac{35}{36}\)

\(x=1\)

a) \(\frac{5}{7}x+0,125=\frac{9}{8}\)

\(\frac{5}{7}x=\frac{9}{8}-0,125\)

\(\frac{5}{7}x=\frac{9}{8}-\frac{1}{8}\)

\(\frac{5}{7}x=1\)

\(x=1:\frac{5}{7}\)

\(x=\frac{7}{5}\)

b) \(x+\frac{7}{12}=\frac{1}{3}-\frac{5}{6}\)

\(x+\frac{7}{12}=-\frac{1}{2}\)

\(x=-\frac{1}{2}-\frac{7}{12}\)

\(x=-\frac{13}{12}\)

http://olm.vn/hoi-dap/question/83032.html?auto=1

\(B=x^3-3x^2+3x\)

\(=\left(x-1\right)^3\)

thay x=11 vào B ta có:
\(B=\left(x-1\right)^3=\left(11-1\right)^3=10^3=1000\)

\(A=x^3+3x^2+3x+6\)

\(=\left(x+1\right)^3+5\)

thay x vào A ta có:

\(A=\left(19+1\right)^3+5=20^3+5=8005\)

\(\left(4x-1\right)^3-\left(4x-3\right)\left(16x^2+3\right)\)

\(=\left(4x\right)^3-3.\left(4x\right)^2.1+3.4x.1^2-1^3-\left(4x-3\right)\left(16x^2+3\right)\)

\(=64x^3-48x^2+12x-1-64x^3-12x-48x^2-9\)

\(=9\)

Vì kết quả là hằng số nên biểu thức trên không phụ thuộc vào x