题目内容
(本题13分)
向量
=(
+1,
),
=(1,4cos(x
+)),设函数
=
(
∈R,且
为常数).
(1)若
为任意实数,求
的最小正周期;
(2)若
在[0,)上的最大值与最小值之和为7,求
的值.
向量
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926917215.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926948192.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926964254.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926980201.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082319092701165.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190927026276.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190927042358.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926948192.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926948192.gif)
(1)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926948192.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190927026276.gif)
(2)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190927026276.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823190926948192.gif)
解: g(x)=mn=a+1+4sinxcos(x+)
=sin2x-2sin2x+a+1
=sin2x+cos2x+a
=2sin(2x+)+a
(1)g(x)=2sin(2x+)+a,T=π.
(2)∵0≤x<,∴≤2x+<
当2x+=,即
x=时,ymax=2
+a.
当2x+=,即x=0时,ymin=1+a,
故a+1+2+a=7,即a=2.
=sin2x-2sin2x+a+1
=sin2x+cos2x+a
=2sin(2x+)+a
(1)g(x)=2sin(2x+)+a,T=π.
(2)∵0≤x<,∴≤2x+<
当2x+=,即
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082319092726072.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082319092743285.gif)
当2x+=,即x=0时,ymin=1+a,
故a+1+2+a=7,即a=2.
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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