Let \( A(6,8) \), \( B(10\cos\alpha, -10\sin\alpha) \), and \( C(-10\sin\alpha, 10\cos\alpha) \) be the vertices of a triangle. If \( L(a,9) \) and \( G(h,k) \) be its orthocenter and centroid respectively, then \( 5a - 3h + 6k + 100\sin2\alpha \) is equal to _____ .