19. What is the cross product w=v1v2 given v1=100,v2=001? 20. What is the dot product of v1 and v2 from the previous problem? 21. What is the length of the vector v2 ? 22. What is the representation of the point p=123 in homogeneous coordinates? What is the representation of the vector v=123 in homogeneous coordinates? 23. What two types of transformations are in the class of rigid body transformations? Give an example 44 matrix for each. 24. Construct the modelview matrix for rotating a cube about its center c=[123]T around the x-axis. (Describe the transformation in terms of one or more of the following: R (degrees, axis) for rotation, S(sx,sy,sz) for scale, T(tx,ty,tz) for translate, H(hx,hy,hz) for shear.) 25. Suppose we are given a model cube centered at the origin with sides length 2 in each dimension. What is the modelview matrix that creates an instance of the cube centered at c with side lengths 1 in each dimension, where c=111? (Use the transformation notation from the previous problem.)