Ответ:\((−x+y)(y+x)=y^2−x^2\).\((−m−n)(m−n)=m^2−n^2\).\((−6b−1)(6b−1)=1−36b^2\).\(\left(\frac{5}{9}ax+\frac{3}{4}bc\right)\left(\frac{5}{9}ax−\frac{3}{4}bc\right)=\frac{25}{81}a^2x^2−\frac{9}{16}b^2c^2\).