已知函数f(x)=ax3+bx2+cx+d为奇函数,且在x=-1处取得极大值2.(Ⅰ)求f(x)解析式;(Ⅱ)过点A(1,
已知函数f(x)=ax3+bx2+cx+d为奇函数,且在x=-1处取得极大值2.(Ⅰ)求f(x)解析式;(Ⅱ)过点A(1,
日期:2014-11-08 17:35:49 人气:1
(Ⅰ)∵f(x)=ax3+bx2+cx+d为奇函数,∴b=d=0,∴f′(x)=3ax2+c,∵f(x)在x=-1处取得极大值2,∴f′(?1)=3a+c=0f(?1)=?a?c=0,解得a=1,c=-3,∴f(x)解析式为f(x)=x3-3x.(Ⅱ)设切点为(x1,y1),则y1=x12?3x1 y1?tx1?1=3x12?3,消去y1得t=-2x13+3x12-3,设h(x)=-2x3+3x2-3,则h′(x)=-6x2+6x=-6x(x-1),由h′(x)>0,得0<x<1,由h′(x)<0,得x<