Ответ:

Используем формулы \((a+b)^2=a^2+2ab+b^2\) и \((a-b)^2=a^2-2ab+b^2\).

  1. \((0.2x+0.3y)^2=0.04x^2+0.12xy+0.09y^2\);
  2. \((0.4b-0.5c)^2=0.16b^2-0.4bc+0.25c^2\);
  3. \(\left(\frac{2}{3}x^3-\frac{3}{4}\right)^2=\frac{4}{9}x^6-x^3+\frac{9}{16}\);
  4. \(\left(\frac{1}{4}c^3-\frac{4}{5}\right)^2=\frac{1}{16}c^6-\frac{2}{5}c^3+\frac{16}{25}\).

Ответ: 1) \(0.04x^2+0.12xy+0.09y^2\); 2) \(0.16b^2-0.4bc+0.25c^2\); 3) \(\frac{4}{9}x^6-x^3+\frac{9}{16}\); 4) \(\frac{1}{16}c^6-\frac{2}{5}c^3+\frac{16}{25}\).