1.å 为f(x)为å¥å½æ°ï¼åc=0.
å¨ï¼1ï¼f(1)ï¼å¤çå线çæç为f'(1)=3a+b
å 为该å线ä¸å·²ç¥ç´çº¿åç´ï¼åæçä¹ç§¯ä¸º-1,å³3a+b=18.
导å½æ°f'(x)=3ax^2+b.æå°å¼ä¸º12,å³a>0,ä¸b=12.æ以a=2.
æ以a=2,b=12,c=0.f(x)=2x^3+12x
å 为g(x)=f(x)?x^2,æ¨æµåºè¯¥æ¯é¤ã
è¥g(x)=f(x)/x^2ï¼åg(x)=2x+12/x>=2â(24)=4â6,å½ä¸ä»
å½2x=12/xæ¶ï¼å³x=â6æ¶ï¼çå·æç«ãå³g(x)çæå°å¼ä¸º4â6.
è¥g(x)=f(x)*x^2,åg(x)=2x^5+12x^3ãåg'(x)=10x^4+36x^2>0.å æ¤g(x)å¨(0,+â)ä¸æ¯åè°å¢ãå æ¤å¨å¼åºé´(0,+â)ä¸æ æå°å¼ã
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