Equations with sin cos tan

Are f, R and x variables? There is no unique solution for 2 equations with 3 variables. Or you simply wants to express R and tan x in terms of the others?

2012-07-29 21:20:46 補充：
(a) f sin x - R cos x = - mg .............(1)
R sin x + f cos x = F ...........(2)
f x (1) + R x (2) we get
f^2 sin x + R^2 sin x = - mgf + RF
so sin x = (RF - mgf)/(f^2 + R^2)......(3)
Similarly, f x (2) - R x (1) we get
f^2 cos x + R^2 cos x = fF + Rmg
so cos x = (fF + Rmg)/(f^2 + R^2).....(4)
tan x = (3)/(4) = (RF - mgf)/(fF + Rmg).
(b)
R^2 cos^2 x = (f sin x + mg)^2
R^2 sin^2 x = (F - f cos x)^2
Adding together and take square root,
R = sqrt [ (f sin x + mg)^2 + (F - f cos x)^2]
= sqrt [ m^2g^2 + 2fmg sin x + f^2 + F^2 - 2Ff cos x]