The given points are A(1,0,0) and B(0,0,1) The direction ratios of the points joining the lines are, (x2−x1),(y2−y1),(z2−z1) So, the equation of the plane for (-1,1,1) is, (x−1)a+(y−0)b+(z−0)c=0 −(x−a)+z=0 π=−x+0y+z+a =0 So, x+y+z=6 The angle between the planes is given by, cosθ=