Trig functions

[wise helm]

Stuck with this question need help. I don't understand the solution

[unkempt crescent]

ok so using the right angled triangle given you know that the diagonal distance times by cosx=6

So you know AD is going to be 6/cosx

and using the circle you know radius is three

So you can use cosine rule to find what AC is

as you know two distances in the triangle

and an angle

So you do that and You find that AC=6cosx

So CD is going to be AD-AC

Which is 6/cosx-6cosx

same as 6secx-6cosx

=6(secx-cosx)

And then for part b you use the show that to get a quadratic with cosx

and then you can use that to find ac

[wise helm]

Thanks