\(\text{Đặt A }=\frac{1}{15}+\frac{2}{45}+\frac{3}{135}+\frac{4}{345}+\frac{5}{759}\)
\(\Rightarrow A=\frac{1}{3.5}+\frac{2}{5.9}+\frac{3}{9.15}+\frac{4}{15.23}+\frac{5}{23.33}\)
\(\Rightarrow2A=2\left(\frac{1}{3.5}+\frac{2}{5.9}+\frac{3}{9.15}+\frac{4}{15.23}+\frac{5}{23.33}\right)\)
\(\Leftrightarrow2A=\frac{2}{3.5}+\frac{4}{5.9}+\frac{6}{9.15}+\frac{8}{15.23}+\frac{10}{23.33}\)
\(\Leftrightarrow2A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{15}+\frac{1}{15}-\frac{1}{23}+\frac{1}{23}-\frac{1}{33}\)(Tại sao ra vậy cứ ib giải thích cho)
\(\Rightarrow2A=\frac{1}{3}-\frac{1}{33}\)
\(\Leftrightarrow2A=\frac{10}{33}\)
\(\Rightarrow A=\frac{10}{33}:2=\frac{5}{33}\)
Chúc bạn học tốt !!!
Cảm ơn bạn nhìu mink cũng chúc bạn hok tốt nhé ! ^^
Đặt A =115+245+3135+4345+5759Đặt A =115+245+3135+4345+5759
⇒A=13.5+25.9+39.15+415.23+523.33⇒A=13.5+25.9+39.15+415.23+523.33
⇒2A=2(13.5+25.9+39.15+415.23+523.33)⇒2A=2(13.5+25.9+39.15+415.23+523.33)
⇔2A=23.5+45.9+69.15+815.23+1023.33⇔2A=23.5+45.9+69.15+815.23+1023.33
⇔2A=13−15+15−19+19−115+115−123+123−133⇔2A=13−15+15−19+19−115+115−123+123−133(Tại sao ra vậy cứ ib giải thích cho)
⇒2A=13−133⇒2A=13−133
⇔2A=1033⇔2A=1033
⇒A=1033:2=533⇒A=1033:2=533
Chúc bạn học tốt !!!
