數學不懂做13

2.
2sin(x/2)sin(a-x/2)
=-2/2 [ cos(x/2+a-x/2) - cos(x/2-a+x/2) ]
=cos(x-a) - cos a

-1≤cos(x-a)≤1
-1 - cos a ≤ cos(x-a) - cos a ≤ 1 - cos a
最大值=1 - cos a

2014-09-16 00:09:26 補充：
謝謝~

但而家我忙緊1D野 0.0

2014-09-18 02:02:07 補充：
Please Read：


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HK~ 回答吧～

5sin²x+√3sinxcosx+6cos²x
= 1 + √3sinxcosx + cos²x
= 1 + √3/2 sin2x + (1 + cos2x)/2
= 3/2 + √3/2 sin2x + 1/2 cos2x
= 3/2 + sin(π/3)sin2x + cos(π/3)cos2x
= 3/2 + cos(2x - π/3)