\(B=-\frac{1}{3}+\frac{1}{3^2}-\frac{1}{3^3}+....+\frac{1}{3^{50}}-\frac{1}{3^{51}}\)
\(3B=-1+\frac{1}{3}-\frac{1}{3^2}+......+\frac{1}{3^{49}}-\frac{1}{3^{50}}\)
\(3B+B=-1+\frac{1}{3}-\frac{1}{3^2}+......+\frac{1}{3^{49}}-\frac{1}{3^{50}}+\left(-\frac{1}{3}+\frac{1}{3^2}-\frac{1}{3^3}+.......+\frac{1}{3^{50}}+\frac{1}{3^{51}}\right)\)
\(4B=-1+\frac{1}{3}-\frac{1}{3^2}+.....+\frac{1}{3^{49}}-\frac{1}{3^{50}}-\frac{1}{3}+\frac{1}{3^2}-\frac{1}{3^3}+.......+\frac{1}{3^{50}}-\frac{1}{3^{51}}\)
\(4B=-1-\frac{1}{3^{51}}\)
cậu chưa tính hết nha vs lại bài này tớ làm đc ùi
