Question

Why is sin(20) = sin(160) = -sin(200) = -sin(340)?

Answer 1

Because they're all the same distance from the x axis on a coordinate plane. Also, remember that in quadrant I, all trig values are positive. In Q II, only sine and cosecant are positive. In Q III, only tangent and cotangent are positive. In Q IV, only cosine and secant are positive. Think of it as All Students Take Calculus.

Answer 2

see.

Explanation:

The value of sin is the same at the same distance from the cuadrant limit of the point. For the case of 20°, we have that the sin is the same in the following case:

As 20 is positive we use the limit cuadrant at 90°. The distance of 20 to 90 is 70. So, sin(20)=sin(90+70)=sin(160).

Also we have that sin(x) is a odd function, so sin(-x)=-sin(x), so

sin(-20°)= -sin(20°)

-sin(-20°)=sin(20°)

-sin(340°)=sin(20°).

and,

sin(-160°)=-sin(160°)

-sin(-160°)=sin(160°)

-sin(200°)=sin(160°)=sin(20°).