- #Ngân giải luôn nà. ^^ không gi lại đề nhá
\(=\left(\frac{5}{4\cdot9}+\frac{5}{9\cdot14}+\frac{5}{14\cdot19}+...+\frac{5}{44\cdot49}\right)\cdot\frac{1-\left(3+5+7+...+49\right)}{89}\)
\(=\frac{1}{5}\cdot\left(\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{19}+...+\frac{1}{44}-\frac{1}{49}\right)\cdot\left(\frac{1-\frac{\left(52\cdot24\right)}{2}}{89}\right)\)
\(=\frac{1}{5}\cdot\left(\frac{1}{4}-\frac{1}{49}\right)\cdot\frac{1-624}{89}\)
\(=\frac{1}{5}\cdot\frac{45}{196}\cdot-\frac{623}{89}\)
\(=-\frac{9}{28}\)
#ĐÚng thì cho ngân ****+điểm