Dear all,

Would appreciate some guidance for this question:

If q = ax + by and r = bx - ay, determine the value of:

 

Dear friends,

I am stuck with this question.

X, Y AND Z are the angles of a triangle and f is a function defined as

f = sin X sin Y sin Z

1) Express f in term of X and Y only
2) Prove that f is a maximum if the triangle is equilateral

Hope someone is able to help me through.
Thank you.