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(1)f(x)=2cos平方x+2√3cosxsinx
=cos2x-1+√3sin2x
=2× (1/2cos2x+√3/2sin2x)-1
=2sin(2x+π/6)-1
最小正周期为π
增区间: 2kπ-π/2≤2x+π/6≤2kπ+π/2
2kπ-2π/3≤2x≤2kπ+π/3
kπ-π/3≤x≤kπ+π/6
即【kπ-π/3,kπ+π/6】,k∈Z
(2) 0f(a)=2sin(2a+π/6)-1
π/6<2a+π/6<5π/6
所以能取到最大值=2-1=1
最小值=2×sinπ/6-1=1-1=0(但取不到)
所以值域为(0,1]