数学 三角函数 高手来帮忙!!!~~

来源:百度知道 编辑:UC知道 时间:2024/06/15 02:32:27
已知函数f(x)=cos²(x/2)-sin²(x/2)+sinx
①求函数f(x)的最小正周期
②当x∈(0,π/4)且f(x)=(4√2)/5时,求f(x+π/6)的值

1. f(x)=cos²(x/2)-sin²(x/2)+sinx
=cosx+sinx
=根号2*(sinx*根号2/2+cosx*根号2/2)
=根号2sin(x+π/4)
最小正周期=2π/1=2π.

2. f(x)=(4√2)/5
根号2sin(x+π/4)=(4√2)/5
sin(x+π/4)=4/5

f(x+π/6)=根号2sin(x+π/6+π/4)

π/4<x+π/4<π/2
cos(x+π/4)=3/5
sin(x+π/6+π/4)=sin(x+π/4)cosπ/6+cos(x+π/4)sinπ/6
=4/5*√3/2+3/5*1/2
=(3+4√3)/10

f(x+π/6)=(3√2+4√6)/10.

cos²(x/2)-sin²(x/2)=cos(2*x/2)=cosx
f(x)=sinx+cosx=√2sin(x+π/4)
所以T=2π/1=2π

f(x)=√2sin(x+π/4)=4√2/5
sin(x+π/4)=4/5
x∈(0,π/4)
x+π/4∈(π/4,π/2)
所以cos(x+π/4)>0
sin²(x+π/4)+cos²(x+π/4)=1
所以cos(x+π/4)=3/5
所以f(x+π/6)=sin(x+π/6+π/4)
=sin(x+π/4)cosπ/6+cos(x+π/4)sinπ/6
=4/5*√3/2+3/5*1/2
=(4√3+3)/10