高一数学三角函数题，在线等！

Question

先把下列各负角的三角比转化为正角的三角比，然后求它的值：
（1）sin(-π/4)
（2）cos(-60°)
（3）tan(-9π/4)
（4）sin(-390°)

有过程，谢谢！！

Answer 1

（1）sin(-π/4)=- sin(π/4)=-√2/2.
（2）cos(-60°)= cos(60°)=1/2.
（3）tan(-9π/4)= tan(-2π-π/4)= tan(-π/4)=- tan(π/4)=-1.
（4）sin(-390°)= sin(-360°-30°)= sin(-30°)=- sin(30°)=-1/2.

Answer 2

（1）：-sin(π/4)= -√2/2
(2):cos(60°)=1/2
(3):tan(π/4)=1
(4):sin(30°)=1/2

Answer 3

(1)Sin(-π/4)=-Sinπ/4=-√2/2
(2)Cos(-60)=Cos60=1/2
(3)tan(-9π/4)=tan(-2π-π/4)=-tanπ/4=-1
(4)Sin(-390)=Sin(-360-30)=-Sin30=-1/2

Answer 4

sin(-π/4)=-sin(π/4)=√2/2
cos(-60°)=cos(60°)=1/2
tan(-9π/4)=-tan(π/4)=1
sin(-390°)=-sin(30°)=1/2

Answer 5

sin(-π/4)
=sin(π/4)
=√2／2