1-1/2+2-2/3+3/4+4-1/4-3-1/3-2-1/2-1=(1-2+4-3-3-3)(1/2-2/3+3/4-1/4-1/3-1/2)=-6.(-1/6)=1

Ta có: \(1-\frac{1}{2}+2-\frac{2}{3}+\frac{3}{4}+4-\frac{1}{4}-3-\frac{1}{3}-2-\frac{1}{2}\)\(-1\)

\(=\left(1+2+4-3-2-1\right)+\left(-\frac{1}{2}-\frac{2}{3}+\frac{3}{4}-\frac{1}{4}-\frac{1}{3}-\frac{1}{2}\right)\)

\(=1+\left(\frac{-3}{2}\right)\)

\(=\frac{-1}{2}\)

a=a chứ = j

\(a.\frac{3}{28}\)

\(b.\frac{9}{5}\)

Bây giờ mình sẽ viết đầy đủ hơn nhé:

a) \(\frac{28^{15}.3^{17}}{84^{16}}=\frac{\left(28.3\right)^{15}.3^2}{\left(28.3\right)^{15}.84}=\frac{9}{84}=\frac{3}{28}\)

b)\(\frac{3^{10}+6^2}{5.3^8+20}=\frac{3^{10}+2^2.3^2}{5.3^8+20}=\frac{3^2.\left(3^8+2^2\right)}{5.\left(3^8+2^2\right)}\)\(=\frac{9}{5}\)

\(\frac{3}{4}+\frac{1}{4}:x=\frac{2}{5}\)

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

\(\frac{1}{4}:x=\frac{-7}{20}\)

\(x=\frac{1}{4}:\frac{-7}{20}\)

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

\(2x\left(x-\frac{1}{7}\right)=0\)

\(=>x=0\)         hoặc  \(x-\frac{1}{7}=0\)

                                             \(x=0+\frac{1}{7}\)

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

Vậy \(x\in\left\{0;\frac{1}{7}\right\}\)

Mình làm câu b thôi nha 

\(\frac{3}{4}\) + \(\frac{1}{4}\) : x = \(\frac{2}{5}\)

 \(1\) : x = \(\frac{2}{5}\)

x = \(1\) * \(\frac{2}{5}\)

x = \(\frac{5}{2}\)

Answer : \(\frac{5}{2}\)

a. x=1

b. x=1

a. x = 1

b. x = 1