> 数学 >
已知函数f(x)=2sinxcos(x+
π
3
)+
3
cos2x+
1
2
sin2x

(1)求函数f(x)的最小正周期;   
(2)求函数f(x)的最大值与最小值;
(3)写出函数f(x)的单调递增区间.
人气:488 ℃ 时间:2019-08-29 06:18:45
解答
f(x)=2sinxcos(x+
π
3
)+
3
cos2x+
1
2
sin2x

=2sinx(cosxcos
π
3
-sinxsin
π
3
)+
3
cos2x+
1
2
sin2x
=sinxcosx-
3
sin2x+
3
cos2x+
1
2
sin2x
=sin2x+
3
cos2x
=2sin(2x+
π
3
),
(1)因为T=
2
=π,所以f(x)的最小正周期为π;
(2)由-1≤sin(2x+
π
3
)≤1,得到-2≤f(x)≤2,
则函数f(x)的最大值为2,最小值为-2;
(3)令2kπ-
π
2
≤2x+
π
3
≤2kπ+
π
2

解得:kπ-
12
≤x≤kπ+
π
12

则f(x)的单调递增区间为:[kπ-
12
,kπ+
π
12
].
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