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已知f(x)=2+log3x,x∈[1,3],求函数y=[f(x)]^2+f(x^2)的值域
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y=(2+log3x)^2+2+log3(x^2)
=(log3x)^2+4log3x+4+2log3x+2
=(log3x)^2+6log3x+6
=(3+log3x)^2-3
x∈[1,3]
log3x∈[0,1]
3+log3x∈[3,4]
(3+log3x)^2∈[9,16]
y=(3+log3x)^2-3∈[6,13]
=(log3x)^2+4log3x+4+2log3x+2
=(log3x)^2+6log3x+6
=(3+log3x)^2-3
x∈[1,3]
log3x∈[0,1]
3+log3x∈[3,4]
(3+log3x)^2∈[9,16]
y=(3+log3x)^2-3∈[6,13]
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