028.13. a) 2\frac{1}{3}a - 1\frac{1}{14}b; б) (0,9x+1\frac{13}{27}y)^2; B) (-1,2x-4\frac{1}{6}y); r) (-2,3a+1\frac{2}{23}b)^2

Решение:

• 028.13. a) \[ \left( \frac{7}{3}a - \frac{15}{14}b \right)^2 = \left( \frac{7}{3}a \right)^2 - 2 \cdot \frac{7}{3}a \cdot \frac{15}{14}b + \left( \frac{15}{14}b \right)^2 = \frac{49}{9}a^2 - \frac{70}{14}ab + \frac{225}{196}b^2 = \frac{49}{9}a^2 - 5ab + \frac{225}{196}b^2 \]
• 028.13. б) \[ (0.9x + \frac{13}{27}y)^2 = (0.9x)^2 + 2 \cdot 0.9x \cdot \frac{13}{27}y + (\frac{13}{27}y)^2 = 0.81x^2 + \frac{23.4}{27}xy + \frac{169}{729}y^2 = 0.81x^2 + \frac{13}{15}xy + \frac{169}{729}y^2 \]
• 028.13. B) \[ (-1.2x - \frac{1}{6}y)^2 = (-(1.2x + \frac{1}{6}y))^2 = (1.2x + \frac{1}{6}y)^2 = (1.2x)^2 + 2 \cdot 1.2x \cdot \frac{1}{6}y + (\frac{1}{6}y)^2 = 1.44x^2 + \frac{2.4}{6}xy + \frac{1}{36}y^2 = 1.44x^2 + 0.4xy + \frac{1}{36}y^2 \]
• 028.13. r) \[ (-2.3a + \frac{2}{23}b)^2 = (-2.3a)^2 + 2 \cdot (-2.3a) \cdot \frac{2}{23}b + (\frac{2}{23}b)^2 = 5.29a^2 - \frac{9.2}{23}ab + \frac{4}{529}b^2 = 5.29a^2 - 0.4ab + \frac{4}{529}b^2 \]