3.6 A circle in the plane R centred at C and of unit radius moves without slipping on the positive x-axis with C moving in the upper half-plane. Write down the parametric equations of the locus of the point P on the circle which coincides with the origin at the initial position of the circle and the parameter being the angle through which the radius CP has turned from the initial vertical position. 3.7 What are the direction cosines of the line joining the point (1, -8, 2) to the point (3, -5,4) in R? 3.8 Find the equation of the plane passing through the point (1, -2, 1) and which is perpendicular to the planes 3x+y+z-2=0 and x-2y+z+4= 0. 3.9 Find the equation of the plane containing the line - 1 - = - y+1 1 Z 3 == 2 4 and which is perpendicular to the plane x + 2y +z = 12. 3.10 A moving plane passes through a fixed point (a, b, c) (which is not the origin) and meets the coordinate axes at the points A, B and C, all away from the origin O. Find the locus of the centre of the sphere passing through the points O, A, B and C.