数学三角函数已知f(x)=2cosxsin(x+π/3)-根号3sinx^2+sinxcosx(1)求fx最小正周期(2)求fx的单调增区间(3)当x∈[0,π/4]时,求fx的值域.

问题描述:

数学三角函数
已知f(x)=2cosxsin(x+π/3)-根号3sinx^2+sinxcosx
(1)求fx最小正周期
(2)求fx的单调增区间
(3)当x∈[0,π/4]时,求fx的值域.

f(x)=2cosxsin(x+π/3)-根号3sinx^2+sinxcosx
=2cosxsin(x+π/3)-2sinx[根号3/2sinx^2-1/2cosx]
=2cosxsin(x+π/3)+2sinxcos(x+π/3)
=2sin(2x+π/3)
最小正周期:Tmin=2π/2=π
(2)
当2kπ-π/2≤2x+π/3≤2kπ+π/2 (k∈Z)时,函数单调递增。此时kπ-5π/12≤x≤kπ+π/12
当2kπ+π/2≤2x+π/3≤2kπ+3π/2 (k∈Z)时,函数单调递减。此时kπ+π/12≤x≤kπ+7π/12
(k∈Z)
(3)
x∈[0,π/4],π/3≤2x+π/3≤5π/6
2x+π/3=5π/6时,有f(x)min=1
2x+π/3=π/2时,有f(x)max=2
函数的值域为[1,2]


(1)
f(x)=2cosxsin(x+π/3)-√3sin²x+sinxcosx
=2cosx[sinx/2+√3cosx/2]-√3sin²x+sinxcosx
=sinxcosx+√3cos²x-√3sin²x+sinxcosx
=2sinxcosx+√3(cos²x-sin²x)
=sin(2x)+√3cos(2x)
=2[(1/2)sin(2x)+(√3/2)cos(2x)]
=2sin(2x+π/3)
最小正周期:T=2π/2=π
(2)
当2kπ-π/2≤2x+π/3≤2kπ+π/2 (k∈Z)时,单调递减,此时kπ-5π/12≤x≤kπ+π/12
当2kπ+π/2≤2x+π/3≤2kπ+3π/2 (k∈Z)时,单调递增,此时kπ+π/12≤x≤kπ+7π/12
单调增区间为:[kπ-5π/12,kπ+π/12];单调递减区间为:[kπ+π/12,kπ+7π/12] (k∈Z)
(3)
x∈[0,π/4],π/3≤2x+π/3≤5π/6
2x+π/3=5π/6时,有f(x)min=1
2x+π/3=π/2时,有f(x)max=2
所以:函数的值域为[1,2]

f(x)=cosxsinx+根号3cosx^2-根号3sinx^2+sinxcosx
=sin2x+根号3cos2x
=2sin(2x+π/3)
(1)T=2π/2=π
(2)2kπ-π/2 kπ-5π/12∴增区间(kπ-5π/12,kπ+π/12),(3)x∈[0,π/4]
2x+π/3∈[π/3,5π/6]
∴f(x)∈[1,2]

化嘛,展开有,f(x)=2cosxsinx+根号3(cos²x-sin²x)=sin2x+根号3cos2x
=2(cos60sin2x+sin60cos2x)=2sin(2x+60)
应该可以做了

(1)f(x)=2cosxsin(x+π/3)-√3sin²x+sinxcosx=2cosx[sinx/2+√3cosx/2]-√3sin²x+sinxcosx=sinxcosx+√3cos²x-√3sin²x+sinxcosx=2sinxcosx+√3(cos²x-sin²x)=sin(2x)+√3cos(2x)=2[(...

f(x)=cosxsinx+根号3cosx^2-根号3sinx^2+sinxcosx
=sin2x+根号3cos2x
=2sin(2x+π/3)
(1)T=2π/2=π
(2)2kπ-π/2 kπ-5π/12∴增区间【kπ-5π/12,kπ+π/12】,k为整数
(3)x∈[0,π/4]
2x+π/3∈[π/3,5π/6]
∴f(x)∈【1,2】

先把能化开的都化开,然后把能配的用公式配好,化简就行了