f(x)=a(1/3x³+bx²+cx)
f'(x) = a(x²+2bx+c)=a(x-m)(x-n)
单调递减区间为【2,5】
则a>0,m=2,n=5
a(x-m)(x-n) = a{x²+(-m-n)x+mn} = a(x²-7x+10),即b=-7,c=10
综上:a的范围(-∞,0),b=-7,c=10
f(x)=a(1/3x³+bx²+cx)
f'(x) = a(x²+2bx+c)=a(x-m)(x-n)
单调递减区间为【2,5】
则a>0,m=2,n=5
a(x-m)(x-n) = a{x²+(-m-n)x+mn} = a(x²-7x+10),即b=-7,c=10
综上:a的范围(-∞,0),b=-7,c=10