令f(x) = 3√x - x根号下无负数,定义域x≥0f'(x) = 3 * 1/(2√x) - 1 = (3-2√x)/(2√x)当0≤x＜9/4时,f'(x)＞0,f(x)单调增x＞9/4时,f'(x)＜0,f(x)单调减x=9/4时,f'(x)=0,f(x)max=3√(9/4)-9/4=9/2-9/4=9/4...