(9) The lines r n + = 0, r n2 + c2 = 0 meet at the point A. Find the equation of the line through A which is at right angles to the line r n + q = 0. (10) If ABC is a triangle whose position vectors of A, B and C are 3i + j, -i+7j, - 3j respectively, find, in normal form, the equations of the medians. (11) The equations of the sides of the sides AB, AD of a parallelo- gram ABCD are r (2i + j) + 5 = 0, r (i-3j) +7=0, and C is the point (1,2). Find the equations of (a) the sides BC, CD; (b) the diagonals AC; BD (12) ABCD is a parallelogram, the position vectors of A, B and C being 4i + 8j, 3i + 6j and -5i-2j respectively. Find (a) the normal vectors of AB and BC: (b) the cartesian equations of AD and CD; (c) the position vector of D; (d) the position vector of the point of intersection of AC and BD;