Найдите значение выражения: 1) a:b-ab, если a=-0,5, b=2/3 2) b+c/b-c, если b=2/7, c=-4/9...

Решите задачу:

$\frac{a}{b} -ab= \frac{a-ab^{2} }{b} = \frac{a(1-b^{2} )}{b} = \frac{a}{b}(1-b^{2}) \\ \\ a= -0.5, b= \frac{2}{3} \\ \\ - \frac{1}{2} : \frac{2}{3}*(1-( \frac{2}{3} )^{2})=- \frac{1}{2} * \frac{3}{2} * \frac{5}{9} =- \frac{5}{12} \\ \\ \\ 2) \\ \frac{ \frac{2}{7} +(- \frac{4}{9}) }{\frac{2}{7} -(- \frac{4}{9})} = \frac{ \frac{18-28}{63} }{ \frac{18+28}{63} } = \frac{10}{63} : \frac{46}{63}= \frac{10}{63} * \frac{63}{46} = \frac{5}{23} \\ \\ \\ 3) \\$ $\frac{ (-0.3)^{2} +( -0.4)^{2} }{-0.3 -(-0.4)} =- \frac{0.09+0.16}{0.7} =- \frac{0.25}{0.7} =- \frac{25}{7} =-3 \frac{4}{7}$