The triangle ABC has sides AB [

] AC [

] and BC [

], as well as cosBaC [

]

a] Write down and simplify a quadratic equation satisfied by

and hence evaluate

b] Express sinBaC in the form

c] Express sinAcB in the form

I have no idea how to solve these, it's the most difficult question I have out of the exam papers and even though I (sort of) understand trigonometry at the moment this is just impossible to me.

Could anyone please help?

For a] I have a value of 8, and this I know to be right

For b] I have

but I don't know how you can express it in the form asked for.

Please could someone help?