$\frac{x^5{y}^7-x^3{y}^9}{x^3{y}^7}=\frac{x^3{y}^7(x^2-y^2)}{x^3{y}^7}=x^2-y^2$
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:
$\frac{4(2+3)}{5(2-3)}=\frac{4\ast 5}{5\ast (-1)}=-4$

$\frac{(3a+3b{)}^2}{3a^2-3b^2}=\frac{(3(a+b){)}^2}{3(a^2-b^2)}=\frac{9(a+b{)}^2}{3(a-b)(a+b)}=\frac{3(a+b)}{a-b}$
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:
$\frac{5\ast (-0,5)}{2}=-\frac{2,5}{2}=-1,25$