uibelion
幼苗
共回答了17个问题采纳率:88.2% 举报
由题意得 f(x)=
1+cos(2x-
4π
3 )
2 +
1-cos(2x-
5π
3 )
2 +
a
2 sinx
=1+
1
2 (cos2xcos
4π
3 +sin2xsin
4π
3 ) -
1
2 (cos2xcos
5π
3 +sin2xsin
5π
3 ) +
a
2 sinx
= 1-
1
2 cos2x+
a
2 sinx = 1-
1
2 (1-2si n 2 x)+
a
2 sinx
= si n 2 x+
a
2 sinx+
1
2
= (si nx+
a
4 ) 2 +
1
2 -
a 2
16
∵a>0,∴对称轴 -
a
4 <0 ,
则当sinx=1时,f(x)取最大值为
a+3
2 ,
由题意得
a+3
2 =3,解得a=3.
1年前
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