f(x)=(根号3sinx+cosx)(根号3cosx-sinx)在区间[0,π⼀2]上的值域是?

2025-04-03 04:13:55
推荐回答(2个)
回答1:

  • f(x)=(√3sinx+cosx)(√3cosx-sinx)

    =2sinxcosx+√3(cos²x-sin²x)

    =sin2x+√3cos2x

    =2(½sin2x+√3/2cos2x)

    =2sin(2x+⅓π)

  • x∈[0,π/2] 

    2x+⅓π=½π→x=π/12 f(x)取得最大值2

    x=½π时 f(½π)=2sin(π+⅓π)=-2sin(⅓π)=-√3为最小值

    f(x)∈[-√3,2]

回答2:

f(x)=(√3sinx+cosx)(√3cosx-sinx)
=3sinxcosx-√3sin²x+√3cos²x-sinxcosx
=2sinxcosx+√3(cos²x-sin²x)
=sin2x+√3cos2x
=2[½sin2x+(√3/2)cos2x]
=2sin(2x+π/3)
x∈[0,π/2],则π/3≤2x+π/3≤4π/3,-√3/2≤sin(2x+π/3)≤1
-√3≤2sin(2x+π/3)≤2
f(x)的值域为[-√3,2]