已知函数f(x)=sin(3π4?x)?3cos(x+π4),x∈R,则f(x)是(  )A.周期为π,且图象关于点(π12,0)

2025-06-24 12:23:02
推荐回答(1个)
回答1:

f(x)=sin(

4
?x)?
3
cos(x+
π
4
)
=sin[π-(x+
π
4
)]-
3
cos(x+
π
4

=sin(x+
π
4
)-
3
cos(x+
π
4

=2[
1
2
sin(x+
π
4
)-
3
2
cos(x+
π
4
)]
=2sin[(x+
π
4
)-
π
3
]
=2sin(x-
π
12
),
∵x∈R,∴x-
π
12
∈R,
∴-1≤sin(x-
π
12
)≤1,
则f(x)的最大值为2;
∵ω=1,∴周期T=
1
=2π;
当x-
π
12
=kπ(k∈Z)时,f(x)图象关于某一点对称,
∴当k=0,求出x=
π
12
,即f(x)图象关于x=
π
12
对称,
故选B