19/04/09 20:29:44.97 RccyPm8I.net
f(θ) = u(θ) * cos(v(θ)) = r * cos(t)
g(θ) = u(θ) * sin(v(θ)) = r * sin(t)
r = u(θ)
t = v(θ)
θ = v^{-1}(t)
r = u(v^{-1}(t))
(1/2) * ∫_{0}^{3*π/5} r^2 dt = (1/2) * ∫_{0}^{3*π/5} [u(v^{-1}(t))]^2 dt
=
(1/2) * ∫_{0}^{3*π/5} [u(v^{-1}(v(θ)))]^2 * v'(θ) dθ
=
(1/2) * ∫_{0}^{3*π/5} [u(θ)]^2 * v'(θ) dθ