题目

已知函数f(x)=sin(2x+π/3)+sin(2x-π/3)+2cos^2x-1
（1）求函数的最小正周期 (2）求f（x）在区间｛-π/4,π/4｝上的最大值和最小值,

提问时间：2020-08-07

答案

f(x)=sin(2x+π/3)+sin(2x-π/3)+2cos^2x-1
=sin2xcosπ/3+cos2xsinπ/3+sin2xcosπ/3-cos2xsinπ/3+cos2x
=2sin2xcosπ/3+cos2x
=sin2x+cos2x
=√2*(√2/2*sin2x+√2/2*cos2x)
=√2*(sin2xcosπ/4+cos2xsinπ/4)
=√2*sin(2x+π/4)
T=2π/2=π
x∈[-π/4,π/4]
2x∈[-π/2,π/2]
2x+π/4∈[-π/4,3π/4]
-1<=√2*sin(2x+π/4)<=√2
f(x)在区间[-π/4,π/4]上的最大值为：√2
f(x)在区间[-π/4,π/4]上的最小值为：-1