Question

Can you use trigonometric functions for any kind of triangle?

Answer 1

It depends on what you mean by "use trigonometric functions".

The Law of Sines tells us that for any triangle: labelled with
`a` = length of the side opposite angle `A`
`b` = length of the side opposite angle `B`
`c` = length of the side opposite angle `C`
we have:

`sinA/a=sinB/b=sinC/c`

(So also, by algebra: `a/sinA = b/sinB = c/sinC`)

The Law of Cosines generalizes the Pythagorean Theorem.
It says that in any triangle labelled as above, we have:
`c^2=a^2+b^2-2ab cosC`
`b^2=a^2+c^2-2ac cosB`
`a^2=b^2+c^2-2bc cosA`