(2012•武清区一模)已知函数f(x)=73sinxcosx+7sin2x-52,x∈R.
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(2012•武清区一模)已知函数f(x)=7
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(Ⅰ)由题意得:函数f(x)=7
3sinxcosx+7sin2x-
5
2=
7
3
2sin2x+7×
1−cos2x
2-
5
2
=7(
3
2sin2x-
1
2cos2x)+1=7sin(2x-
π
6)+1.
令 2kπ-
π
2≤2x-
π
6≤2kπ+
π
2,k∈z,可得 kπ-
π
6≤x≤kπ+
π
3,k∈z,
故函数的增区间为[kπ-
π
6,kπ+
π
3],k∈z.
令 2kπ+
π
2≤2x-
π
6≤2kπ+
3π
2,k∈z,可得 kπ+
π
3≤x≤kπ+
5π
6,k∈z,
故函数的减区间为[kπ+
3sinxcosx+7sin2x-
5
2=
7
3
2sin2x+7×
1−cos2x
2-
5
2
=7(
3
2sin2x-
1
2cos2x)+1=7sin(2x-
π
6)+1.
令 2kπ-
π
2≤2x-
π
6≤2kπ+
π
2,k∈z,可得 kπ-
π
6≤x≤kπ+
π
3,k∈z,
故函数的增区间为[kπ-
π
6,kπ+
π
3],k∈z.
令 2kπ+
π
2≤2x-
π
6≤2kπ+
3π
2,k∈z,可得 kπ+
π
3≤x≤kπ+
5π
6,k∈z,
故函数的减区间为[kπ+
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