就是求值通式是 (-1)^(n + 1) * n * 1/(2*n - 1) * 1/(2*n + 1) = (-1)^(n + 1) * ( 1/(2*n -1) + 1 / (2 * n + 1) /4求和,n从 1 到 6算起来就是 (1/1 + 1/3 - 1/3 - 1/5 + 1/5 + 1/7 - 1/7 - 1/9 + 1/9 + 1/11 - 1/...