1/(2*3)+1/(3*5)+1/(4*7)+...+1/[(n+1)(2n+1)]= 1/6 + 1/(3*5)+1/(4*7)+...+1/[(n+1)(2n+1)]= 1/6 + 1/2 * {1/(3*2.5)++1/(4*3.5)+...+1/[(n+1)(n+0.5)] }< 1/6 + 1/2 * {1/(3.25*2.25)+1/(4.25*3.25)+...+1/[(n+1.2...