数学题!!!!关于函数

已知函数f(x)=cos눀(x+π/12)+1/2sin2x求f(x)的最值求f(x)的单调增区间
2026年09月22日 02:44
有3个网友回答
网友(1):

f(x)=cos²(x+π/12)+1/2sin2x
=[1+cos(2x+π/6)]/2+1/2sin2x
=1/2+1/2sin(π/3-2x)+1/2sin2x
=1/2+sin(π/6)cos(π/6-2x)
=1/2+1/2sin(2x+π/3)

(1)sin(2x+π/3)=1→x=kπ+π/12时,
所求最大值为:1;
sin(2x+π/3)=-1→x=kπ-5π/12时,
所求最小值为:0.

(2)单调递增时,
2kπ-π/2≤2x+π/3≤2kπ+π/2
→kπ-5π/12≤x≤kπ+π/12;
即x∈[kπ-5π/12, kπ+π/12];
单调递减时,
2kπ+π/2≤2x+π/3≤2kπ+3π/2
→kπ+π/12≤x≤kπ+7π/12,
即x∈[kπ+π/12, kπ+7π/12]。

网友(2):

函数f(x)=(1+cos(2x+pi/6))/2+1/2sin2x=0.5(1+sin(2x+pi/3))
-1<=sin(2x+pi/3)<=1=>0<=f(x)<=1
调增区间:2kpi-pi/2<=2x+pi/3<=2kpi+pi/2=>kpi-(5pi/12)<=x<=kpi+pi/12 k为整数

网友(3):

降次和倍角公式即可