已知函数f(x)=cosx(sinx-cosx)+1(Ⅰ)求函数f(x)的最小正周期;(Ⅱ)当x∈[-π2,0]时,求函数f

2024-10-29 18:54:45
推荐回答(1个)
回答1:

(Ⅰ)∵f(x)=sinxcosx-cos2x+1
=

1
2
sin2x-
1+cos2x
2
+1
=
1
2
sin2x-
1
2
cos2x+
1
2

=
2
2
sin(2x-
π
4
)+
1
2

∴函数f(x)的最小正周期为T=
2
=π.
(Ⅱ)∵x∈[-
π
2
,0],
∴-
4
≤2x-
π
4
≤-
π
4

∴-1≤sin(2x-
π
4
2
2

?
2
+1
2
2
2
sin(2x-
π
4
)+
1
2
≤1,
?
2
+1
2
≤f(x)≤1;
当2x-
π
4
=-
π
2
时,即x=-
π
8
时,函数f(x)取到最小值
?
2
+1
2

当2x-
π
4
=-
4
,即x=-
π
2
时,函数f(x)取到最大值1.