a) \(\sqrt{\frac{4}{9}}-\left(-\frac{1}{1}\right)^2+\frac{1}{4}=\frac{2}{3}-1+\frac{1}{4}=\frac{11}{12}-=-\frac{1}{12}\)

b) \(\left(\frac{-1}{2}+\frac{1}{3}\right).\frac{4}{5}+\left(\frac{2}{3}+\frac{1}{2}\right):\frac{5}{4}=\left(-\frac{1}{6}\right).\frac{4}{5}+\left(\frac{7}{6}\right).\frac{4}{5}\)

\(=\left(-\frac{1}{6}+\frac{7}{6}\right).\frac{4}{5}=\frac{6}{6}.\frac{4}{5}=\frac{4}{5}\)

a, Xét : \(\left(2x-1\right)^4=1\Leftrightarrow\orbr{\begin{cases}2x-1=1\\2x-1=-1\end{cases}\Leftrightarrow\orbr{\begin{cases}x=1\\x=0\end{cases}}}\)

Xét : \(\left(81.2\right)\left(x-2\right)^2=1\Leftrightarrow162\left(x-2\right)^2=1\Leftrightarrow\left(x-2\right)^2=\frac{1}{162}\)

\(\orbr{\begin{cases}x-2=\sqrt{\frac{1}{162}}\\x-2=-\sqrt{\frac{1}{162}}\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{36+\sqrt{2}}{18}\\x=\frac{36-\sqrt{2}}{18}\end{cases}}\)

a) -7/20= (-1/4)+ (-1/10)= (-3/20)+ (-1/5)= (-1/20)+(-3/10)

b)-7/20= 1/20 -2/5=1/10 -9/20=3/20 -1/2

Bài này dễ mà QAQ

Ta có : \(\frac{-7}{20}=\frac{\left(-1\right)+\left(-6\right)}{20}=\frac{\left(-2\right)+\left(-5\right)}{20}=\frac{\left(-3\right)+\left(-4\right)}{20}\)

Do đó \(\frac{-7}{20}=\frac{-1}{20}+\frac{-6}{20}=\frac{-1}{20}+\frac{-3}{10}\)

\(\frac{-7}{20}=\frac{-2}{20}+\frac{-5}{20}=\frac{-1}{10}+\frac{-1}{4}\)

\(\frac{-7}{20}=\frac{-3}{20}+\frac{-4}{20}=\frac{-3}{20}+\frac{-2}{10}\)

b) \(\frac{-7}{20}=\frac{1-8}{20}=\frac{2-9}{20}=\frac{3-10}{20}\)

Do đó \(\frac{-7}{20}=\frac{1}{20}-\frac{8}{20}=\frac{1}{20}-\frac{4}{10}\)

\(\frac{-7}{20}=\frac{2}{20}-\frac{9}{20}=\frac{1}{10}-\frac{9}{20}\)

\(\frac{-7}{20}=\frac{3}{20}-\frac{10}{20}=\frac{3}{20}-\frac{1}{2}\)

\(\left[1-\left(\frac{3}{4}-\frac{2}{3}\right)\right]-\left[1-\left(\frac{5}{3}-\frac{1}{4}\right)\right]-\left[1-\left(\frac{4}{3}+\frac{3}{4}\right)\right]\)

\(=\left[1-\frac{3}{4}+\frac{2}{3}\right]-\left[1-\frac{5}{3}+\frac{1}{4}\right]-\left[1-\frac{4}{3}-\frac{3}{4}\right]\)

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

\(=\left(1-1-1\right)+\left(-\frac{3}{4}-\frac{1}{4}+\frac{3}{4}\right)+\left(\frac{2}{3}+\frac{5}{3}+\frac{4}{3}\right)\)

\(=-1-\frac{1}{4}+\frac{11}{3}=\frac{29}{12}\)

[3-(8-11)]-[-2+(-15+3)]

=[3+3]-[-2+(-15+3)]

=[3+3]-[-2+-12]

=6-[-2-12]

=6+14

=20

b) Xét \(x=0\)thì \(0+\left|y\right|< 20\)=> \(\left|y\right|< 20\Rightarrow y\in\left\{0;\pm1;\pm2;...;\pm19\right\}\)gồm 39 giá trị

Xét x = \(\pm1\)thì y \(\in\left\{0;\pm1;\pm2;\pm3;...;\pm18\right\}\)gồm 37 giá trị

....

Xét x = \(\pm\)18 thì y \(\in\){0; \(\pm\)1} 

Xét x = \(\pm19\)=> y = 0 , có 1 giá trị

Có tất cả : 2(1 + 3 + ... + 37) + 39 = 761(cặp số)

\(\frac{\left(2^6\right)^2.\left(3^4\right)^3.34}{2^{13}.3^9.17}=\frac{2^{12}.3^{12}.2}{2^{13}.3^9}=3^3=27\)

thanks