函数f(x)=3sin(x+10°)+5sin(x+70°)的最大值是( ) A.5.5 B.6.5 C.7 D.8
问题描述:
函数f(x)=3sin(x+10°)+5sin(x+70°)的最大值是( )
A. 5.5
B. 6.5
C. 7
D. 8
答
f(x)=3sin(x+100)+5sin[(x+100)+600]
=3sin(x+100)+5sin(x+100)cos60°+5cos(x+100)sin60°
=
sin(x+10°)+11 2
cos(x+10°)5
3
2
=
sin(x+100+∅),其中tan∅=
(
)2+(11 2
)2
5
3
2
5
3
11
≤
=7
(
)2+(11 2
)2
5
3
2
故选C.