Finding cos and sin from tan?

Give the expression for one of the three functions sin θ, cos θ, or tan θ, with θ in the first quadrant. Find expressions for the other two functions. Your answer will be algebraic expressions in terms of x.

a) x = 2 cos θ

b) x = 9 tan θ

What are we suppose to do? I don't get what the x in front of the equation and the variables such as "2" and "9" in front of the cos and tan mean. And how would we solve it for the other two trig functions? Please help me with this and show your work. Thank you so much!