(1)对称轴x=2a∵f(x)在[1,2]上单调增∴2a≤1∴a≤1/2(2)设x1∈(0,+∞),则-x∈(-∞,0)∴f(-x)=x²-x∵函数f(x)在R上是偶函数∴f(x)=f(-x)=x²-x 定义域为(0,+∞)∴f(x)=x
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