f(x)=x-3√(x+5)根号下无负数：x+5≥0定义域x≥-5f'(x) = 1 - 3/[2√(x+5)]= {√(x+5)-3/2}/√(x+5)当x∈【-5,-11/4)时,f'(x) ＜0,f(x)单调减；当x∈（-11/4,+∞)时,f'(x) ＞0,f(x)单调增.最小值f(-11/4) = -11/4-3...