Question:
Use the symmetric and periodic properties of the sine, cosine and tangent functions to establish the following results.





Attempt:
I don't know how to start

Hello,

For the first one, there are two ways imho :
- sketch a trigonometrical circle and you will see that this relation is true
- use the formula sin(a-b)=sin(a)cos(b)-sin(b)cos(a)

For the second one, use the periodicity :
- the sine function is 360-periodic. Hence

- As the sine function is an odd function, sin(-x)=-sin(x)
- and you retrieve the first relation