Let \( k \in \mathbb{R} \) and \( D = \{(r, \theta) : 0<r<2, 0<\theta<\pi\ \). Let \( u(r, \theta) \) be the solution of the following boundary value problem \[ \frac{\partial^2 u}{\partial r^2} + \frac{1}{r} \frac{\partial u}{\partial r} + \frac{1}{r^2} \frac{\partial^2 u}{\partial \theta^2} = 0, \quad (r, \theta) \in D, \] \[ u(r, 0) = u(r, \pi) = 0, \quad 0 \leq r \leq 2, \] \[ u(2, \theta) = k \sin(2\theta), \quad 0<\theta<\pi. \] If \( u\left(\frac{1}{4}, \frac{\pi}{4}\right) = 2 \), then the value of \( k \) is equal to ………. (round off to TWO decimal places).