Ta có : M=1/3+1/15+1/35+...+1/2499
=> M=1/1.3+1/3.5+1/5.7+...+1/49.51
=>2M=2/1.3+2/3.5+2/5.7+...+2/49.51
=>2M=1-1/3+1/3-1/5+1/5-1/7+...+1/49-1/51
=>2M=1-1/51
=>2M=50/51
=> M=50/51:2
=> M=25/51
Vậy M=25/51
Mọi người tk giúp mik nha mik đang âm điểm nek !!!
\(\frac{1}{5}\)+\(\frac{1}{15}\)+...+\(\frac{1}{2499}\)=\(\frac{1}{2}\)(\(\frac{2}{3.5}\)+\(\frac{2}{5.7}\)+...+\(\frac{2}{49.51}\))
=\(\frac{1}{2}\)(\(\frac{1}{3}\)-\(\frac{1}{5}\)+\(\frac{1}{5}\)-\(\frac{1}{7}\)+...+\(\frac{1}{49}\)-\(\frac{1}{51}\))
=\(\frac{1}{2}\)(\(\frac{1}{3}\)-\(\frac{1}{51}\))
=\(\frac{1}{2}\).\(\frac{16}{51}\)
=\(\frac{8}{51}\)
Kết quả của mik là M=25/51
Bạn nhớ tk nha mik giải cẩn thận rồi . Mik cảm ơn nhìu !!!
M=\(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+......+\frac{1}{49.51}\)
2M=\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+.....+\frac{2}{49.51}\)
2M=\(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{51}\)
2M=\(\frac{1}{1}-\frac{1}{51}\)
2M=\(\frac{50}{51}\)
M=\(\frac{25}{51}\)
k mk vs