2.8 2/3x=8-9分之7x

考察一般项第k项： (2k)2/[(2k-1)(2k+1)] =4k2/(4k2-1) =(4k2-1+1)/(4k2-1) =1 +1/(4k2-1) =1+ 1/[(2k-1)(2k+1)] =1+ ?[1/(2k-1) -1/(2k+1)] 22/(1×3)+ 42/(3×5) +62/(5×7)+ 82/(7×9) +102&