Difference of squared distances. Determine whether the difference of the squared dis- tances to two fixed vectors p and q, defined as f(x) = ||r p||? |- a|l, is linear, affine, or neither. If it is linear, give its inner product representation, i.e., an n-vector a for which f(r) = a"x for all r. If it is affine, give a and b for which f(r) = a"x +b holds for all r.