Распредели выражения по группам

\(\dfrac{1}{2}x^2-\dfrac{5}{7}b\) , \(12x-\dfrac{1}{x^2}\) , \(ab^2c^3-\dfrac{5}{x}ab^2c^3\) , \(\dfrac{99}{101x^2}\) , \(\dfrac{a+b}{a^2}+\dfrac{a-b}{a^2}\) , \(\dfrac{x^3}{x^2}-65x\) , \(\dfrac{x^3}{x^2}-\dfrac{65x^2}{x^3}\) , \(7,5ab-18ba\) , \((85a):(5a^2)\) , \(\dfrac{18a^2}{x^2}-\dfrac{x^2}{18a^2}\) , \((5a^4):(a^2)\) , \((x):(5)\) , \(\dfrac{a}{15}\)