已知函数y=1⼀2cos平方x+[(根号3)⼀2]sinxcosx+1,x属于R

2024-11-23 06:03:52
推荐回答(1个)
回答1:

1/2=sin(π/6),√3/2=cos(π/6),因此可对表达式化简:
y=(1/2)(cosx)^2+(√3/2)sinxcosx+1
=cosx[sin(π/6)cosx+cos(π/6)sinx]+1
=sin(x+π/6)cosx+1 ………………………………………………………(1)
sin(2x+π/6)=sin(x+π/6+x)=sin(x+π/6)cosx+cos(x+π/6)sinx ………(2)
1/2=sin(π/6)=sin(x+π/6-x)=sin(x+π/6)cosx-cos(x+π/6)sinx ………(3)
(2)+(3)可得:sin(x+π/6)cosx=[sin(2x+π/6)]/2+1/4 ……………(4)
把(4)代入(1)继续化简:
sin(x+π/6)cosx+1
=[sin(2x+π/6)]/2+1/4+1
=[sin(2x+π/6)]/2+5/4

因此:y=[sin(2x+π/6)]/2+5/4

(1)y取最大值时,sin(2x+π/6)=1,即2x+π/6=2kπ+π/2,求得x=kπ+π/6(k∈Z),
因此所求x的集合为:{x|x=kπ+π/6(k∈Z)}

(2)由函数表达式y=[sin(2x+π/6)]/2+5/4可知变换顺序:
sinx → sin(x+π/12) → sin[2(x+π/12)]=sin(2x+π/6) → [sin(2x+π/6)]/2 → [sin(2x+π/6)]/2+5/4
即将函数y=sinx的图像先整体左移π/12个单位,然后横向压缩一倍(即左右压缩),之后纵向压缩一倍(即上下压缩),最后整体上移5/4个单位,就可得到题设函数的图像。

或者:sinx → sin2x → sin(2x+π/6) → [sin(2x+π/6)]/2 → [sin(2x+π/6)]/2+5/4
即将函数y=sinx的图像先横向压缩一倍,然后整体左移π/12个单位,之后纵向压缩一倍,最后整体上移5/4个单位,也可得到题设函数的图像。