设二次函数f(x)=ax
2-4x+c(x∈R)的值域为[0,+∞),
+
则的最大值是( )
A.
B. 2
C.
D. 1
人气:483 ℃ 时间:2019-09-05 08:38:08
解答
由二次函数f(x)=ax2-4x+c(x∈R)的值域为[0,+∞),得a>0△=16−4ac=0,∴ac=4,a>0,c>0,1c+1+9a+9=a+9c+18(c+1)(a+9)=a+9c+18a+9c+13=1+5a+9c+13≤1+529ac+13=1+525=65,当且仅当a=9c时取等号,由ac=4a...
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