(a²+ab)/(a+b)
a-b=(a-b)(a+b)/(a+b)
(x-y)/[x(x+y)]
=y(x-y)²/[xy(x+y)(x-y)]
(x+y)/[y(x-y)]=x(x+y)²/[xy(x+y)(x-y)]
1/a=12ab²c/(12a²b²c)
1/(4a²b)=3bc/(12a²b²c)
1/(6ab²c)=2a/(12a²b²c)
x分之y,y分之x,x+y分之xy
y/x=y²(x+y)/[xy(x+y)]
x/y=x²(x+y)/[xy(x+y)]
xy/(x+y)=x²y²/[xy(x+y)]