1/(2X5)+1/(5X8)+1/(8X11)+...+1/((3n-1)*(3n+2))=1/3*(1/2-1/5+1/5-1/8+1/8-1/11+...+1/(3n-1)-1/(3n+2))=1/3*(1/2-1/(3n+2))=n/(6n+4)2^2/(1X3)+4^2/(3X5)+6^2/(5X7)+...+(2n)^2/((2n-1)*(2n+1))因为(2n)^2/((2n-1...