f(x) = sinx / x ,f '(x) = (x cosx - sinx ) / x² = cosx ( x - tanx) / x²x∈(π/4,π/2),f '(x) < 0,f(x)单减,f(x) 的最大值 f(π/4) = √2/2 / (π/4)最小值 f(π/2) = 1/(π/2)估值：区间长度π/4,∴...