Answer :
Bạn hay cho đề ra rồi mình giúp nhé.
#_Học tốt
quá dễ
\(A=\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}\)
\(A=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+\frac{1}{11.13}\)
\(A=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}\right)+\frac{1}{2}.\left(\frac{1}{5}-\frac{1}{7}\right)+\frac{1}{2}.\left(\frac{1}{7}-\frac{1}{9}\right)+\frac{1}{2}.\left(\frac{1}{9}-\frac{1}{11}\right)+\frac{1}{2}.\left(\frac{1}{11}-\frac{1}{13}\right)\)
\(A=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{13}\right)\)
\(A=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{13}\right)\)
\(A=\frac{1}{2}.\left(\frac{10}{39}\right)\)
\(A=\frac{5}{39}\)
help me, pls. Sắp đến giờ nộp bài rồi, các bn giúp mình với
