25/51
因为1/(1*3)=(1/1-1/3)/2,1/(3*5)=(1/3-1/5)/2,1(5*7)=(1/5-1/7)/2...1(49*51)=(1/49-1/51)/2
所以1/(1*3)+1/(3*5)+1/(5*7)+…+1/(49*51)=(1-1/3+1/3-1/5+1/5...+1/49-1/51)
=(1-1/51)/2=25/51
楼上2个答案不对
25/51
因为1/(1*3)=(1/1-1/3)/2,1/(3*5)=(1/3-1/5)/2,1(5*7)=(1/5-1/7)/2...1(49*51)=(1/49-1/51)/2
所以1/(1*3)+1/(3*5)+1/(5*7)+…+1/(49*51)=(1-1/3+1/3-1/5+1/5...+1/49-1/51)
=(1-1/51)/2=25/51
楼上2个答案不对