330. Charges with surface densities σ1 and σ2 are uniformly distributed on two coaxial infinite cylinders of radii R and 2R (Fig. 26). It is required: 1) using the Ostrogradsky-Gauss theorem: find the dependence E (r) of the electric field strength on the distance for three regions: I, II and III. Take σ1 = -σ, σ2 = 4σ; 2) calculate the strength E at a point remote from the axis of the cylinders at a distance r, and indicate the direction of the vector E. Take σ = 30 nC / m2, r = 4R; 3) build a graph of E (r).