10、积的价格为b元,当造价最低时,锅炉的底面直径与高的比为( >kavU42VRUsA. B. C. D.y6v3ALoS89解读:如图,设圆柱的底面半径为R,高为h,则V=πR2h.设造价为y=2πR2a+2πRhb=2πaR2+2πRb·=2πaR2+,∴y′=4πaR-.M2ub6vSTnP令y′=0,得=.答案:C二、填空题7.函数f(x>=x2-lnx的最小值为________.解读:由得x>1,0YujCfmUCw由得0在x=1时取最小值f(1>=-ln1=.sQsAEJkW5T答案: