Where does the sine rule come from?

For the mathematical puritans out there the sine rule derives from the following:

(you really don’t need to know this)

Find “a” KNOWING the angle A and length b and c.

Redraw the diagram

Find Y in the triangle I 

Use trigonometry which tells us that `sin\ theta=(O)/H`

`sinA=Y/b`

Therefore: `Y=bsinA`                                                    

Find “a” in triangle II

Use trigonometry which tells us that `sin\ theta=(O)/H`

`sinB=(bsinA)/a`                                         

Therefore  `a=(bsinA)/sinB`

Or  `a/sinA=b/sinB`  (the sine rule)

But again we emphasise that you really don’t need this.