$\frac{x^5y^7 - x^3y^9}{x^3y^7} = \frac{x^3y^7(x^2 - y^2)}{x^3y^7} = x^2 - y^2$
если x = −0,2, y = 0,5:
$(-0,2)^2 - 0,5^2 = 0,04 - 0,25 = -0,21$

$\frac{4a^2 - 36}{5a^2 - 30a + 45} = \frac{4(a^2 - 9)}{5(a^2 - 6a + 9)} = \frac{4(a - 3)(a + 3)}{5(a - 3)^2} = \frac{4(a + 3)}{5(a - 3)}$
если a = 2:
$\frac{4(2 + 3)}{5(2 - 3)} = \frac{4 * 5}{5 * (-1)} = -4$

$\frac{(3a + 3b)^2}{3a^2 - 3b^2} = \frac{(3(a + b))^2}{3(a^2 - b^2)} = \frac{9(a + b)^2}{3(a - b)(a + b)} = \frac{3(a + b)}{a - b}$
если $a = \frac{1}{3}, b = -\frac{1}{6}$:
$\frac{3(\frac{1}{3} - \frac{1}{6})}{\frac{1}{3} + \frac{1}{6}} = \frac{1 - \frac{1}{2}}{\frac{2}{6} + \frac{1}{6}} = \frac{\frac{1}{2}}{\frac{3}{6}} = \frac{\frac{1}{2}}{\frac{1}{2}} = 1$

$\frac{20x^2 - 140xy + 245y^2}{4x - 14y} = \frac{5(4x^2 - 28xy + 49y^2)}{2(2x - 7y)} = \frac{5(2x - 7y)^2}{2(2x - 7y)} = \frac{5(2x - 7y)}{2}$
если 2x − 7y = −0,5:
$\frac{5 * (-0,5)}{2} = -\frac{2,5}{2} = -1,25$