2x=5y;y/x=2/5;3x的平方-xy+2有的平方/晓得平方+5xy-3y的平方=(3x²-xy+2y²)/(x²+5xy-3y²)=(3-y/x+2(y/x)²)/(1+5y/x-3(y/x)²)=(3-2/5+2×(4/25))/(1+5×(2/5)-3×(4/25))=73/25/(63/25...