B=1/2(C-A)=1/2(3x²-2xy-y²-x²+2xy+y²)=1/2(2x²)=x²,
E=B-2C=x²-2(3x²-2xy-y²)=-5x²+2xy+y²
由折叠可知D所对的面为B,F所对的面为E.
所以D=x²,F=-5x²+2xy+y²
B=1/2(C-A)=1/2(3x²-2xy-y²-x²+2xy+y²)=1/2(2x²)=x²,
E=B-2C=x²-2(3x²-2xy-y²)=-5x²+2xy+y²
由折叠可知D所对的面为B,F所对的面为E.
所以D=x²,F=-5x²+2xy+y²