P(x)=(x-1)^2*A(x)+2x-3、P(x)=(x-1)^2*(x-2)*C(x)+R の2式から、
(x-1)^2*A(x)+2x-3=P(x)=(x-1)^2*(x-2)*C(x)+R　⇔　(x-1)^2*A(x)+2x-3-(x-1)^2*(x-2)*C(x)=R
⇔　(x-1)^2*{A(x)-(x-2)*C(x)}+2x-3=R