9. If

Solution:

Given,

   

And, we know by definition that

   

opposite side/ adjacent side

Thus, by comparison

Opposite side

   

and adjacent side

   

To find the hypotenuse, we know that by Pythagoras theorem that

Hypotenuse² = opposite side² + adjacent side²

⇒ Hypotenuse

   

So, by definition

   

opposite side/ Hypotenuse

   

And,

   

adjacent side/ Hypotenuse

   

Now,

After substituting for

   

and sin

   

we have

Hence Proved.