函数f(x)=alnx+bx²+3x的极值点为x1=1,x2=2,则a= ,b=

函数f(x)=alnx+bx²+3x的极值点为x1=1,x2=2,则a= ,b=
函数f(x)=alnx+bx²+3x的极值点为x1=1,x2=2,则a= ,b=

函数f(x)=alnx+bx²+3x的极值点为x1=1,x2=2,则a= ,b=
f(x)=alnx+bx²+3x
求导
f'(x)=a/x+2bx+3
带入
x=1 x=2得
a+2b+3=0
a/2+4b+3=0
解得
a=-2
b=-1/2

f(x)=alnx+bx²+3x
f'(x)=a/x+2bx+3 极值点为x1=1,x2=2,
f'(1)=a+2b+3=0
f'(2)=a/2+4b+3=0
解得 a=-2 b=-1/2

先求导，a/x+2bx+3=0
a+2b+3=0
a/2+4b+3=0
a=-2
b=-1 /2

f'(x)=a/x +2bx+3
在极值点，导数为零
即f'(1)=a+2b+3=0
f‘(2)=a/2 +4b+3=0
解得a=-2,b=-1/2

tt