**Convention**:

**Positive**-valued angle means

**anti-clockwise rotation**(or forward moving direction).

**Negative**-valued angle means

**clockwise rotation**(or reverse moving direction).

Diagram 1 below shows the convention in graphic form.

Diagram 1

Besides rotational direction, what does the "sign" of the angle has on the numerical value of their trigonometric operation?

Is cos 60

^{0}= cos (- 60

^{0}) ?

How about its sine counterpart?

Is sin 60

^{0}= sin (- 60

^{0}) ?

The diagrams below will provide the answers to the above two questions.

Diagram 2: Cosine function

In diagram 2, we can see that the amplitude of the cosine for +60

^{0}and -60

^{0}remains the SAME.

That is to say,

**whether the angles are positive or negative,**

__cosine__function of these angles are the same.Let's look at the Sine operation of negative angles (Diagram 3).

Diagram 3: Sine function

Here in diagram 3, we see a difference.

**The numerical value of**

__sine__operation on positive and negative angle differs by the sign. They are DIFFERENT!sin 60

^{0}=

**-**sin (-60

^{0})

In conclusion,

**cos A = cos (-A) and**

sin A = - sin (-A).

sin A = - sin (-A).

As such tan A = - tan (-A) since tan A = sin A / cos A.

"-" and "+" can be confusing.

However, do note that it is the learner's duty to master this concept.

Pressurised? Fear not!

Mindset change will do the trick. "I love maths as it is interesting!"

.

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