函数y=2-"根号下-x²+4x"的值域是()?A.[-2,2]B.[1,2]C.[0,2]D.[-根2,根2]
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函数y=2-"根号下-x²+4x"的值域是()?A.[-2,2]B.[1,2]C.[0,2]D.[-根2,根2]
函数y=2-"根号下-x²+4x"的值域是()?
A.[-2,2]B.[1,2]C.[0,2]D.[-根2,根2]
函数y=2-"根号下-x²+4x"的值域是()?A.[-2,2]B.[1,2]C.[0,2]D.[-根2,根2]
-x^2+4x=-(x-2)^2+4 所以选C
选C
-x²+4x
=-(x²-4x+4)+4
=-(x-2)²+4
所以0≤-x²+4x≤4
于是
0≤根号下-x²+4x≤2
0≤2-根号下-x²+4x≤2
所以选C