^ đó là mủ đấy bạn tại mình ko tháy hình mủ nên lấy hình trong máy tính casio
1) \(\frac{1}{2}x-\frac{2}{5}=\frac{-1}{5}\)
\(\frac{1}{2}x=-\frac{1}{5}+\frac{2}{5}\)
\(\frac{1}{2}x=\frac{1}{5}\)
\(x=\frac{1}{5}:\frac{1}{2}\)
\(x=\frac{2}{5}\)
Vậy \(x=\frac{2}{5}\)
2) \(\frac{4}{9}-\frac{7}{8}x=-\frac{2}{3}\)
\(\frac{7}{8}x=\frac{4}{9}-\left(-\frac{2}{3}\right)\)
\(\frac{7}{8}x=\frac{4}{9}-\frac{-6}{9}\)
\(\frac{7}{8}x=\frac{10}{9}\)
\(x=\frac{10}{9}:\frac{7}{8}\)
\(x=\frac{80}{63}=1\frac{17}{63}\)
Vậy \(x=1\frac{17}{63}\)
3) \(B=1+2+2^2+2^3+...+2^{2016}+2^{2017}\)
Ta có : \(2B=2.\left(1+2+2^2+...+2^{2016}+2^{2017}\right)\)
\(2B=2+2^2+2^3+2^4+...+2^{2017}+2^{2018}\)
\(2B-B=\left(2+2^2+2^3+2^4+...+2^{2017}+2^{2018}\right)-\left(1-2-2^2+2^3+...+2^{2016}+2^{2017}\right)\)
\(B=2+2^3+2^4+2^5+...+2^{2017}+2^{2018}-1-2-2^2-2^3-...-2^{2016}-2^{2017}\)
\(B=2^{2018}-1\)