Question

write sin(2arccos(x/3)) as an algebraic expression

Answer 1

first, use the double angle formula
sin(2x) = 2 sin(x)cos(x)

Answer 2

http://www.wolframalpha.com/input/?i=sin%282arccos%28x%2F3%29%29

Answer 3

so,
sin(2arccos(x/3)) = 2 sin(arc cos(x/3)) cos(arccos(x/3))

Answer 4

http://www.algebra.com/algebra/homework/Trigonometry-basics.faq.question.247773.html

Answer 5

That should help you ;)

Answer 6

@RadEn then how do I make the triangle?