已知函数f(x)=2sin²x+√3 sin2x-1
2个回答

f(x)=2sin^x+根号3sin2x-1

=-(1-2sin^2x)+根号3sin2x

=-cos2x+根号3sin2x

=2sin(2x-π/6)

所以

f(x-π/6)=2sin(2x-π/3-π/6)

=2sin(2x-π/2)

=-2cos2x

所以f(x-π/6)+4sinx+1

=-2cos2x+4sinx+1

=-2(1-sin^2x)+4sinx+1

=2sin^2x+4sinx-1

=2(sin^2x+2sinx+1-1)-1

=2(sinx+1)^2 -3=a

又因为x∈[π/6,π/2]

(sinx+1)^2=1/2(a+3)

sinx∈[1/2,1]

sinx+1∈[3/2,2]

(sinx+1)^2∈[9/4,4]

所以a∈[9/4,4]