\ begin {alinear*} b (x) & = p (x) - a (x) d (x)\ & = p (x) - a (x) (r (x) p (x) + s (x) q (x))\\ & = p (x) - a (x) r (x) p (x) - a (x) s (x) q (x)\ & = p (x) (1 - a (x) r (x)) + q (x) (- a (x) s (x))...\ begin {alinear*} b (x) & = p (x) - a (x) d (x)\ & = p (x) - a (x) (r (x) p (x) + s (x) q (x))\\ & = p (x) - a (x) r (x) p (x) - a (x) s (x) q (x)\ & = p (x) (1 - a (x) r (x)) + q (x) (- a (x) s (x))\ final {alinear*}